tonight, live from havana. historic change as the u.s. flag rises over the american embassy for the first time in over half a century. a day many thought they'd never live to see. also, could a surprise challenger shake up the race for president? as party jitters grow over hillary clinton, speculation now swirling around names like biden and gore. found alive. a young firefighter pulled from the rubble after that devastating blast in china. chemical weapons. the frightening new turn in the fight against isis. u.s. officials believe terrorists are now unleashing deadly agents. and bracing for impact. after that unsettling news about a godzilla el nino whipping up monster storms, new concerns about exactly what's to come. "nightly news" begins right now.

>> announcer: this is "nbc nightly news with lester holt." reporting tonight from havana. good evening. we're coming to you this evening from the charming and historic habana vieja plaza de san francisco de asis in havana just across from the harbor. cuba is a country physically less than 100 miles from american soil but it feels a lot closer socially and politically tonight and that provoked some tearful and joyous reactions today among many cubans. for the first time in 54 years the american flag was hoisted above the united states embassy here. the ceremonial reopening of the embassy led by secretary of state john kerry marks the re-establishment of diplomatic relations between the two countries while ending years of hostility. there was no question the day was historic. the debate continues at home, however, over whether it sets the right course. leading our coverage is nbc's andrea mitchell.

>> reporter: on a day when symbols matter, the stars and stripes raised over the u.s. embassy in havana, ending a feud that began more than a half century ago. >> this is truly a memorable occasion. a day for pushing aside old barriers and exploring new possibilities. >> reporter: the last time an american secretary of state came to cuba, franklin roosevelt was president. john kerry rewrote that history today. not present, fidel castro seen yesterday on his 89th birthday with leftist allies from bolivia and venezuela. today kerry also tried to meet average cubans, even checking out the old cars in the historic section of havana. but it would take more than a flag raising and a visit to heal these political wounds. kerry is being criticized today for not inviting cuban political dissidents to the embassy ceremony. instead he met them privately at the u.s. diplomatic residence. >> why not have them come there and, you know, participate in the flag raising? >> well, they're going to participate, andrea. i don't buy the notion

that there's a distinction. that was a government-to- government event, but we're meeting with them. i'm here for whatever number of hours. and during that time we have invited a large group to come and partake and meet. and plus i'm meeting with a whole cross-section of civil society from cuba. so you know, i just don't accept that. >> reporter: despite unresolved issues the younger generations in havana have new hope today. alicia echevarria is an actress and recent university graduate. >> it's very good to be part of this process. i mean, everything is changing and you're part of that. it's great. ♪ >> reporter: isaac delgado, a musician and aspiring record producer, hopes to experiment with blends of cuban and u.s. music. >> for me this is special. when you mix the culture of united states and the culture of cuba, we have a very special result. >> reporter: today there was

tough talk by both sides. each accusing the other of human rights abuses. and when i asked john kerry what american tourists will be able to come here when they can come here without restrictions he said first he needs to make progress on the easier things. lifting the embargo, of course, that requires an act of congress, not anytime soon, lester. >> andrea mitchell tonight. by the way, later in the broadcast i speak with those marines who were part of that flag raising today. the decades of bad blood between the u.s. and cuba not only divided our countries but also families caught in the middle. now as relatives who are split between our two nations watch the flag raising today, they are filled with new hope of reunion. we get that story from nbc's gabe gutierrez. >> reporter: it was a sight many cubans thought they would never see, a moment that shook the world of abel fernandez guarea. >> i really don't know how to express it. but i felt something

good. i felt something was happening. >> reporter: in havana he watched today's ceremony live with his wife. miles away in miami so did his father, ramon. >> now i have hope. >> reporter: hope, he says, to see and hug his son. ramon left cuba 20 years ago. he still remembers the day he said good-bye to his only son, then 16. "he asked me dad, will you come back? i said yes. but i didn't." instead he missed many moments, including his son's wedding. "it hurts very much," he says, "but such is life." >> we need to share lots of things we have missed along these years. >> reporter: for years abel has wanted to join his father but his visa to the u.s. was never approved. he and his wife hope after today things will be easier. >> it's going to be easier. and not only for us but for our

families and our relatives and friends and everyone. >> reporter: for now they settle for phone calls. >> okay. i love you more. >> reporter: but today they were able to share something more. ♪ >> it's a great moment because the war is over. >> today i think we are closer. today i feel closer to him. >> reporter: that's just one of many families wondering what all these changes will mean for them. and lester, you've been speaking with people here on the streets of havana. no one anticipates that more than 50 years of hostility will evaporate overnight. but as secretary kerry said today, it's a start. >> there's a lot of hope and expectation. thanks very much. appreciate it. the american flag flies temporarily tonight outside cuba's foreign ministry as an apparent gesture in recognition of this historic day. and that's where i spoke to foreign minister bruno rodriguez. among the topics, opposition to

the new u.s.-cuban relationship. >> as you know, there are influential american politicians who argue that this was a gift, what we saw today was a gift to cuba without receiving anything in return in terms of human rights reform. what's your answer to that? >> well, as secretary kerry pointed out, that it's not to know when. firstly it's a bilateral relationship, and we have to build it from both sides on the basis of a good faith. because of the national interests, the interests of american and cuban citizens. it's not a gift. >> the foreign minister also impressed on me cuba's desire to end the u.s. economic embargo which he says has damaged his country. there's another big story we're following tonight. it's increasing concern among some of the democratic party over hillary clinton's recent struggles. that has led to

speculation about a possible run by vice president biden. now there's word some are trying to push a new challenger in her direction, former vice president al gore. chuck todd is in iowa talking to democrats. >> if someone told me six months ago that i wouldn't be supporting hillary now, i would have never believed them. >> there you go. >> reporter: at the iowa state fair today, growing concerns about the clinton campaign among democrats that i talked to. >> what concerns you about hillary clinton? >> there's always something. >> reporter: today that something is another story about classified information on the private server she used for official state department e-mail. democrats are concerned about the drip, drip, drip. >> i think when those issues come up you just face it head on and say this is where we made mistakes. >> so she owes you a better explanation? >> absolutely. we're smarter than that. >> reporter: then there's the rise of bernie sanders. this week, a poll showing him ahead of hillary clinton in new hampshire.

all making democrats nervous enough to suggest al gore or joe biden should get in. >> i was excited to hear that. i'm sorry to hear that's just a rumor. >> reporter: as for biden he's seriously thinking about a run but telling allies he's less than 50-50. hoping to shore up support, clinton's campaign rolled out an endorsement by influential former iowa senator tom harkin. a not-so-subtle signal to gore and biden that it may be too late. >> we don't need any alternatives right now. we have i think one of the best candidates we've ever had in hillary clinton. >> reporter: republicans are here today too. jeb bush working the grill. testing an outsider message. >> i haven't been in washington, d.c. i wouldn't know how to drive. i can barely get from dulles to senator grassley's office. >> reporter: and telling nbc's kelly o'donnell he refuses to exploit voter anger. >> if it's about appealing to people's angst, i don't think i'm going to win. if it's about saying we can rise up again, we can fix these things, i believe i'm going to

be a pretty formidable candidate. >> reporter: i'm here by the way in clear lake, iowa. i've got a rowdy group of democrats behind us, a big democratic cattle call. hillary clinton, martin o'malley, bernie sanders all speaking here tonight. i've got to tell you, lester, spend a little time in iowa and you realize hillary clinton is a fragile front-runner. speaking of fragile front-runners, i've got donald trump one on one this weekend in person right before he makes his way to the state fair. >> one not to miss. chuck, thanks. we'll see you on sunday for "meet the press." in china we are getting a clearer picture tonight of the incredible scope of devastation from that wave of explosions in a major port city near beijing. and as a massive search and rescue operation continues for the missing, a piece of hope today. a sign of life in a smoldering wreckage. nbc's ian williams is there. >> reporter: amid the smoldering debris it's hard to imagine anyone survived. but today rescue workers found

19-year-old firefighter zho ti, badly injured but alive. he was rushed to the hospital. he's expected to recover. others were not so lucky. at least 21 firefighters were killed in the blast. more than a third of all fatalities and a dozen still missing. people today posted flyers, trying to find missing loved ones. the blast was captured on video by american dan van doren. he thought he was going to die. >> it was just monumental. i thought it was a small nuclear bomb. i thought it was a nuclear bomb going off in my face. that's what it looked like. >> reporter: and this surfaced today, a dash cam video showing the blast and its powerful shock waves. it's at a warehouse complex owned by a company called ruihai logistics. dangerously, perhaps illegally close to apartment towers on a busy highway. drone footage shows apartment buildings heavily damaged. there is speculation the explosion may have been inadvertently caused by firefighters spraying water on volatile chemicals.

it's not yet known exactly which chemicals were stored at the site. a team of biochemical specialists arrived here in tianjin. today, though, local officials still admit they don't know precisely what toxic brew they're dealing with. authorities say residents have nothing to fear, but officials took no chances. apartments a mile from the fire were being evacuated. when we tried to film it, we were stopped and asked to leave. the fear and uncertainty here is growing. ian williams, nbc news, tianjin. let's tell you about now a frightening new turn in the fight against isis. word that the militants are suspected of unleashing chemical weapons in recent attacks. further testing is being done, but officials believe this is a dangerous new escalation. our chief foreign correspondent richard engel has late details. >> reporter: u.s. officials tell nbc news they now believe isis used mustard gas, a banned chemical weapon used twice in recent weeks in both iraq and syria.

the most recent attack was three days ago in northern iraq against u.s.-allied kurdish forces. a top kurdish official tells nbc news projectiles containing a chemical agent were fired from isis-controlled territory. no kurdish fighters were killed but several suffered difficulty breathing, vomiting, and patchy burns. secretary of state kerry in cuba today had this to say about isis. >> they've crossed many red lines already and they're one of the most ruthless and dangerous terror groups that any of us have ever imagined. >> reporter: 27 years ago saddam hussein murdered 5,000 kurds with mustard gas and other chemical weapons. this time they're allegedly victims of terrorists. u.s. officials say this is not a red line moment and it's unlikely to significantly change u.s. policy. the u.s. is already bombing isis. but the use of chemical weapons

does change the dynamics on the battlefield. the kurds don't have gas masks. they may need them as isis is apparently willing to use any weapon it can. lester? >> nbc's richard engel tonight. thanks. up next we'll tell you about a monster change in the forecast. the so-called godzilla el nino headed to the u.s. we're going to show you how that ripple effect will be felt from east to west including a surprise in store this winter. also an unprecedented warning from the palace to the paparazzi tonight over the safety of prince george.

tonight the western u.s. is caught between extremes. monsoons bringing torrential rain and flooding while much of the region is also baking in triple-digit temps. and with a so-called godzilla el nino we've been telling you about brewing in the pacific, months of historic weather chaos could be ahead, affecting the rest of the country, too. nbc news national correspondent miguel almaguer has our report. >> reporter: it rolled in with fury. this las vegas monsoon wreaking havoc. lightning sparking fires, torrential rain triggering flooding. a fast-moving summer storm that could be a preview of what's to come this winter. >> el nino's definitely a double-bladed sword. it will provide drought relief but it also provides an awful lot of mayhem and damage. >> reporter: nasa climatologist bill paxter says a monster el nino is moving in our direction.

scientists can see it in the water. the rising temperatures associated with el nino in the pacific may seem small, roughly three degrees. but for forecasters it's enough to predict big changes in our weather all across the country. el nino could mean the warmest year ever on record. heat waves right now already baking much of the country. where there's extreme fire and drought now we could see epic floods and mudslides. el nino could also mean more hurricanes in the pacific and fewer of them in the atlantic. the southern u.s. could be looking at a washout while much of the northern swath of the country may be warmer and drier. >> so we're kayaking down the street in los angeles and they're playing golf in february in minneapolis. >> reporter: el nino promising weather whiplash. during a year of unforgiving extremes. miguel almaguer, nbc news, los angeles. we're back in a moment with

some of the day's other big headlines including word of a tragedy in a famous american park.

a tragic turn of events in yosemite national park. two young campers were killed when a large oak tree limb fell on their tent crushing them inside. the park says falling branches are actually quite common and they are not linking this accident to the drought in the region. kensington palace has a warning for the paparazzi. keep your distance from prince george. palace officials issued a letter complaining that photographers are going to extreme lengths to snap pictures of the 2-year-old prince, going so far as to use other kids to draw george into view on playgrounds. it also mentions that cars have pursued the family, which draws to mind of course the circumstances surrounding the death of george's grandmother, princess diana. and it's a girl for our own jenna bush hager and her

husband, henry hager. poppy louise hager joins older sister mila. former president george w. bush shared a photo of his granddaughter explaining poppy was named after her great grandfather, former president george h.w. bush, who was nicknamed poppy as a child. congratulations. when we come back, the promise made 54 years ago in cuba finally fulfilled by three united states marines. accident at semite.===take v=th

street===next cle=== thnews isn secretary of state kerry walked through this plaza a bit earlier today. he met shopkeepers and people on the streets getting a flavor of cuban culture. before we leave you tonight we want to get back to that story of the three u.s. marines who lowered the flag at the embassy in 1961. they were back today to do the honors raising that flag as the embassy reopened. great guys, and i had the honor to spend some time with them. they are forever marines, who returned to havana to answer the call of duty one more time. >> when you started hearing relations between the u.s. and cuba were being repaired did you begin to dream this might be possible? >> i've been dreaming for 20 years. >> 54 years ago you gentlemen promised to return to havana and hoist the flag over the united states embassy that you lowered

on that january day long ago. promise made. promise kept. >> reporter: and as there was the day they lowered it in 1961, there was a crowd today to witness history. to see it go up, to hear the "star-spangled banner," what were you thinking? >> it was beautiful going up today. i've never seen a better flag. >> we three brought it down. and we three got to put it back up. >> reporter: the last time they were in havana, they became a part of history. they were guards at the american embassy when the u.s. broke off diplomatic relations with cuba and the three men were given a difficult job. >> how did this come about? were you ordered to do this? did you volunteer? >> i guess us guys volunteered. >> we were it. >> reporter: leaving cuba was emotional. >> were you sad to leave? >> oh, yeah. we got on the car ferry and were heading out to harbor and we're trying to listen to

the news or the radio. and they were all blocked except one station. and they played "exodus." the cubans did. so we whipped out our 4th of july sparklers and waved back. >> reporter: coming back was equally moving. what was it like to be a part of the other side of this history? >> there's only three marines that's done it on both ends. and here we are. >> to me it was an honor to be there on this side putting the flag back up. ♪ >> reporter: today these marines are part of history once again, helping two nations open a new chapter. ♪ >> a promise kept on a historic day here in cuba. that is going to do it for us on this friday night. for all of us at nbc news including our entire team in havana, thank you for watching. good night. and have a good weekend. falling te limb.onight,the inve

>> per two children killed in yosemite by a falling tree limb. an investigation into this camping trip tragedy. >> we will get to that story in a moment, but first, breaking news in the north bay. firefighters are racing to put out a grass fair near san raphael. it is likely a case of arson. this is a live picture. you can see on the right of your screen, a lot of smoke. we got off the phone with the marin county sheriff's department. a group of boys were seen

running from this location. there were about six of them wearing white polo shirts. one building is threatened by the fire and roads are closed around the fall. we will bring you more information as it becomes available. we are also following more developing information from yosemite. park rangers say a branch fell on a tent while two children slept inside at the popular upper pines campground. it appears to be a freak accident. michelle roberts has been following the story and joins us now from the newsroom. this is just what they said before, a terrible accident. >> it's so awful. it happened at a popular campground. a from an oak tree. you can see where the branch broke off. they are not saying how old or where the children were from. this happened very early, about 5:00 this