goodnight. breaking news tonight. a gunman armed with an assault rifle opens fire on passengers on a high-speed train to paris. a dramatic takedown by americans on board. a u.s. military service member among the wounded. also a major freefall on wall street. stocks plunge 500 points. over 1,000 in a week. fears of a global economic slowdown triggering the worst sell-off in years. state of emergency. a deadly fire disaster growing rapidly tonight as we learn about the young firefighters lost on the front line. and the crowd goes wild for donald trump. tens of thousands expected tonight. so many people they had to move the event to a football stadium. "nightly news" begins right now. >> announcer: from nbc

news world headquarters in new york, this is "nbc nightly news" with lester holt. good evening. we'll get to the impact of that big sell-off on wall street in a moment. but right now we've got details coming in from france where two americans are injured and are being called heroes in a shooting attack aboard a high-speed train from amsterdam to paris. without the intervention of the americans we're told casualties could have been far worse. french officials say a man opened fire with an automatic weapon in what's being called a possible terrorist attack. nbc's keir simmons is on the story. >> reporter: the attack left three passengers injured including two americans. at least one of them a member of the u.s. military. a woman's bag is left splattered with blood after a gunman reportedly opened fire aboard a high-speed train from amsterdam to paris. the french interior minister at the scene said the two injured americans intervened to stop the attacker, who was reportedly armed with a

kalashnikov rifle, an automatic pistol, and a knife. without their intervention, he said, we could have faced a terrible tragedy. cellphone video shows an unidentified man carried across the platform. witnesses describe the terror on board the train. >> translator: i asked what happened. he told me we have to stop because there's a man who had a kalashnikov in first class. >> reporter: another passenger told nbc news, "i saw the man who was shot in the neck stumble. he dropped his duffel bag right in the seat across from me, and he collapsed on the floor." anti-terrorist officials are leading the investigation into what happened. ammunition piled up on the platform. forensic experts on the scene look for evidence. and tonight a suspect has been arrested. french media say he is a 26-year-old moroccan. >> once again, france in the headlines. >> reporter: eight months ago terrorist gunmen opened fire at the paris office of "charlie hebdo" magazine, killing 12 people. today the french

president expressed his solidarity to those injured and their loved ones in what could have been a deadly assault, stopped by the quick action of what the french are calling courageous americans. keir simmons, nbc news, london. there is also late word of a deadly shooting at a federal building here in new york during the evening rush. a federal law enforcement official says a gunman walked inside this afternoon and opened fire, hitting a private security guard before turning the gun on himself. the motive is unclear. the building houses a federal detention center and immigration court, among other things. now to today's drama on wall street. if your pension or your 401(k) is invested in the stock market, it's a good bet you lost money today. in fact, you've probably been losing it for days. an already lousy week on wall street ended today with a huge sell-off. the dow jones industrial average plummeting 530 points, or 3%. that's a 1,000-point loss for the week. and it happened against the backdrop of what indications

show to be an improving u.s. economy, helping us make sense of it and what it could mean to your bottom line, here's nbc's tom costello. >> reporter: on wall street today a rout capping off a month of pain with americans' pensions and 401(k)s in a sea of red. >> the dow jones industrial average having its worst day in four years today, dropping 528 points. this is the worst week for the dow since 2011. >> reporter: the dow, s&p, and nasdaq all in a nose dive. the dow has now slid 10% from its all-time high. the biggest reason for the sell-off is a world away from america's main streets. the chinese economy is slowing fast. and we live in an interconnected global economy. >> how bad is china? >> it's worse than you think. whatever you might think, it's worse. >> reporter: last week china devalued its currency to make its exports cheaper, sparking concerns of a currency war with the u.s.

>> we don't know whether or not they have the capability to contain their own problems. there's been a lot of overinvestment there. there's been a lot of bad investment. there's been a lot of corruption in the investment that's been made there. we don't quite understand how it all plays out. >> reporter: also weighing on the markets, the dramatic slide in oil price now at a six-year low below $40 a barrel. good news at the pump where prices are expected to drop to $2 a gallon by the end of the year. already $2.19 at this station in dallas. >> the cheaper the better. >> reporter: but it's bad news for big oil companies, many of which are now laying off employees. big oil company stocks have been hit especially hard on wall street. so what should americans with money in the stock market do now? experts say it may be best to wait it out. >> you don't want to panic. panic is not an investing strategy. you also don't -- you shouldn't feel compelled to make a decision about investing at a moment in time. in other words, what do i do right now? >> reporter: the situation in china and the stock market sell-off may convince the fed not to raise interest rates as expected next month.

in fact, some experts think they may now be on hold through the end of the year. lester? >> tom, thanks very much. let's bring in cnbc's sue herera. all of those things tom just ticked off, the chinese economy, oil prices, those are going to be in effect monday as they were today. are we look at a short flash or a sustained longer-term slump? >> i think it is probably going to be longer-term because our market is watching the chinese officials so closely we're kind of dependent on how they decide to manage their own economy and their own market. also, august is traditionally a very volatile month and it certainly is proving that out to be true. so the analysts i'm talking to say at least the next few weeks expect more volatility and probably more down side activity in the market. and then we're going to be going into the fall, which also traditionally has some risk in it as well. so you have to really figure out what your risk tolerance is if you're going to be in the stock market, lester. >> sue herera tonight. thank you.

tonight the president has declared a federal emergency in washington state. a major disaster as wildfires continue to explode. growing again overnight. threatening homes. the situation is getting so desperate officials there are now asking for volunteers to help in the fight. nearly 100 fires now burning in the west. our national correspondent miguel almaguer reports from the front lines. >> reporter: in parts of washington state devastation. more evacuations, more homes lost every day. >> it's all burning up. and we just -- we don't have the resources available. >> reporter: with smoke billowing into the sky, unhealthy air alerts issued in several states, whipping winds are fueling fast-moving fires, burning over 100 square miles in just over one day. >> the wind is blowing every direction. like a tornado, picking up really fast. >> reporter: in the burn zone firefighters struggle to stay ahead of the flames. pilots have been making drops here all day long, but

the conditions are now blinding. it is really affecting the firefight here. last night they paused for a procession. a tribute for the three firefighters killed this week. we now know the fire made a 180 degree shift. a vehicle dropping off an embankment, tumbling downhill. richard wheeler, a ten-year veteran on the fire lines, leaves behind his wife. andrew zajac was married to a fellow firefighter. his grandfather says he loved the outdoors. >> oh, very proud. he was a -- he was a good boy. real good boy. >> reporter: tom zbyszewski was just 20. the only child. the son of a firefighter. >> he was a special kid. you know, we're really going to miss tom. >> reporter: tonight they honor the dead by continuing the fight. for the first time in washington state history they're asking for

volunteers who can operate heavy machinery. alex thomason spent thousands of dollars to buy a fire truck. now the full-time lawyer spends his spare time protecting the community. >> if we can save one person's home, this is absolutely worth it. so here we are. >> reporter: crews tell us tonight they are worried about the next six hours. that's when the red flag warning will end. if there is any good news here, it does promise better weather over the weekend. lester? >> miguel almaguer, thank you. hurricane danny has strengthened to a major category 3 storm in the atlantic. it's packing maximum sustained winds of 115 miles per hour. still about 900 miles away from the islands in the eastern caribbean. forecasts show it could weaken to a tropical storm by the time it arrives there on monday. but it bears watching. tonight tens of thousands are expected to turn out for the biggest rally we've seen yet on the campaign trail. so many clamoring to

hear donald trump speak in alabama they've had to move the event to a football stadium that seats well over 30,000. nbc's katy tur is in mobile. >> reporter: some traveling hundreds of miles. others bused here. politics and a show. in week they move to ladd peebles stadium, capacity 40,000. so far 36,000 have rsvped. and if they all show up, it will be the biggest event so far this political season. all fueled by donald trump's emotional appeal. hammering on points

like border security, birth right citizensh citizenship. >> minority voters are not a key electorate in the republican primary process. and so for those republicans who fear that donald trump's rhetoric is too exchange, i'm not sure that it will hurt him within the primary. >> reporter: during a lunch rush at mobile's famous oyster house, politics the art of looking for trouble finding it everywhere, diagnosing it wrongly, and applying unsuitable recommendingdyerecommend did he, the perfect police. >> i'm looking for somebody to cut government down to size. the people are tired of it. >> reporter: trump on stage right now getting loud applause for overturning or re-enter prettying the 14th amendment which would get rid of birth right citizen ship and

as for the crowd size 36,000 expected, but more like 20,000. >> much more on all things trump, clip top a clinton and the race for the whus on met t "meet the press" sunday. confirmation tonight from the white house that the second in command of isis was killed in a u.s. air strike last week. it happened while he was in a car driving near mosul, an isis stronghold in iraq. there's a desperate scene playing out overseas as hundreds of refugees are rushing the macedonian border from greece, clashing violently with police. yesterday a state of emergency was declared to handle the surge. our cameras were there when hundreds of refugees came ashore in greece just days ago. tens of thousands who made the journey in recent weeks, most of them fleeing isis and the killing in syria. tensions between north and south korea may be at a breaking point this evening. and u.s. forces may be caught in the middle. north korea, a nuclear power and

often prone to saber rattling, says it is mobilizing for war, claiming that south korea is provoking a showdown. nbc's ian williams has our report from seoul, south korea. >> reporter: north korea is threatening war over these loudspeakers. south korea recently started using them again to broadcast propaganda across the dmz, a provocation north korea says. on state television threats of military action unless the speakers are removed. the deadline now just hours away. kim jong-un, the north's unpredictable dictator, today declared what he called a quasi-state of war and ordered his troops to prepare for battle. the demilitarized zone where north and south korea face off is the most fortified place on earth. the south, backed by 28,000 u.s. troops. u.s. forces have been there since the korean war. they take part in frequent military exercises with the south, including one under way now. another provocation, the north says.

the loudspeaker dispute triggered an exchange of artillery fire thursday. the two koreas' most serious clash in years. hundreds of border villages were forced to evacuate to underground shelters. this is one of the shelters. it's a pretty heavy bombproof door. this woman told me she was used to heated rhetoric but the shelling made her nervous. with good reason. >> north korea has nuclear weapons. the whole korean peninsula's a tinderbox. so we want to stabilize things. that's very much in our interests. >> reporter: but tonight south korea was saying it will strike back hard at any provocation from the north. ian williams, nbc news, seoul. a lot more to tell you about here. still ahead tonight, breaking the habit. how a family of five successfully did what so many people are finding impossible right now. cutting the sugar. and later, a family of a different kind cooling off on a hot summer day.

>> there's bears in the pool! >> there sure are. imagine seeing this in your back yard.

we've heard a lot this summer about americans trying to dramatically cut back on sugar and just how hard it is to do. but tonight you're going to meet the one family of five that did it together. our national correspondent kate snow reports on their big challenge. >> reporter: for deirdre diggins dinner-time used to

mean a crazy rush to get some food in her teenagers. >> i'd be throwing food in my mouth and heading out. i was tired of the food preparation. and i think a lot of moms feel that way. >> reporter: but after her youngest was diagnosed with diabetes she reached out to nutritionist terry rhodes for help, starting with the pantry. >> i'd just take it out and say have as much as you want. >> reporter: first tip, get rid of those snack bins. >> this comes in at 27 grams of sugar. so within this amount they've now exceeded the daily recommended sugar intake. >> reporter: the american heart association says we should be eating between three and nine teaspoons of added sugar a day. but the average american is eating 22. the sugar association says the evidence is lacking for these recommendations and that sugar in moderation can be part of a balanced diet. >> for breakfast i would have i would say a handful of jelly beans. it was far more than a handful. >> reporter: naeemah clark didn't just quit sugar. like a growing number of americans she posted

her goals on facebook. >> because i have said it out loud and my facebook friends knew and my friends at work were telling other people, like i know that i'm -- i can stick to this, and i feel good. i'm not grumpy about it. >> just look at how that difference in sugar is. >> reporter: in minnesota terry taught deirdre another tip. don't let your kids dictate the shopping list. fewer than four grams a sugar and greater than three grams of fiber is terry's general guideline. it was tough on deirdre's kids at first. >> we all were kind of like what? >> ice cream just went away? >> yeah. that was tough. that was really -- i miss that a lot. >> reporter: we had them document the first few days of the diet. >> i'm tired. >> feeling kind of tired. >> i keep saying i'm tired all the time. >> reporter: but around day 4 everyone noticed a change. >> i feel good. >> my energy level was more -- i felt better all day. >> reporter: it's a work in progress but deirdre

is hoping she can make the new habits stick. kate snow, nbc news, chanhassen, minnesota. we're back in a moment with a warning from the cdc. what you may be doing wrong if you wear contacts.

the cdc has a warning for the nearly 41 million americans with contact lenses. bad habits are endangering your eyes. a new survey of adults who wear contacts shows at least half sleep with them in. more than half don't change out the solution in their cases. and about a third have rinsed their contacts in microbe-laden tapwater. perhaps it's no surprise that a third have gone to the doctor complaining of eye pain. and how's this for a way to earn free tuition for a semester? an incoming freshman at ball state university in muncie, indiana sinking a half-court shot to earn a free ride for the first half of the school year. believe it or not, the school says it's the second time in three years a student hit that shot for free tuition for the semester.

and any kid playing in the street knows when the ball gets away sometimes you've just got to let it go. that wasn't an option in toledo when a storm knocked a giant 250-pound red ball loose from an art installation, and no gutter was big enough to stop it. it rolled over a car and it bent a street sign before it was chased down. when we come back, some pools are too hot. some pools are too cold. but this one, just right. thproms at mai=nt cse=he ws ne.

we end tonight with what has to be the video of the day or >> it's a mom taking her kids for a dip in a back yard pool just like any other family except you probably wouldn't want to play a game of marco polo with them. here's stephanie gosk. >> reporter: on a hot summer day when the woods in new jersey can really get unbearable, what's a mother of five supposed to do? >> there's bears in the pool! >> reporter: but the two children who normally get to use this pool aren't exactly happy about it. >> they took my floaty! >> i know. we'll buy a new one. >> reporter: and there are some practical concerns about a family of bears in the backyard

pool. >> when the mother gets out, i'm afraid she's going to collapse the pool. >> reporter: the videos posted by the basso family are irresistible. in part because the bears are so relatable. >> two are fighting. >> they're playing. they're brothers and sisters. >> reporter: some roughhousing, some taking turns on the slide, going down and up the wrong way. look at this moment. a cub makes the age-old mistake of pestering mom when all she wants to do is relax. the penalty, a roughly enforced pool timeout. at some point it just gets to be too much for the bassos. the pool is a mess. the toys are chewed up. >> oh, that's not good. >> reporter: and the pool filter is ripped out. despite all the fun they are having -- >> the police are there. >> reporter: -- it's time for the bear family to go. >> maybe they're scared of the police. >> reporter: busted one too many times perhaps. >> oh, my goodness. >> reporter: stephanie gosk, nbc news, new york. >> i've got nothing else that can top that. that's going to do it for us on

a friday night. i'm lester holt for all of us at nbc news thank you for watching, have a great weekend and good night. plginmortha500p . . a stock market melt down. the dow continues to drop, plunging more than 500 points, the biggest drop since 2008. >> i'm jessica aguire. the bad news is hurting the local tech industry and thousands of 401(k)s. business and tech reporter scott budman is standing by to talk about the market sell off and the impact here. live downtown? san jose and the economy is

doing so well here locally that workers are being brought in from across the country to build more homes and more office buildings. >> that's right. it's quite busy here behind me and once this is done, another one will be waiting. >> they come from across the country staying in local hotels as they build homes in san jose. >> it is booming right now. >> he heads a local building and trade council. there is construction work in san jose to last until 2018, but they have to chip in workers to meet the demand. >> we are hiring workers in the bay area all the way from sacramento and the valley a. >> this and city manager