The derailment occurred on the first day Amtrak trains began using the new inland route between the Washington cities of Tacoma and Olympia, part of a 154 million euro ($181 million) project to cut travel time.
Amtrak reported in a statement that 78 passengers and five crew members were aboard the train when it crashed. Some motorists were injured but none died, police said.
The train was travelling from Seattle to Portland using a new route when it derailed on a curve.
"We've launched a full go team with all the different types of experts", said an NTSB spokesperson.
"We moved down to the trains that were more seriously damaged that had flipped upside down, and luckily I had brought a headlamp with me from my auto, because the trains were all dark, and there was a lot of wreckage, and some of them were upside down or the roofs were caved in", Konzelman said.
"All of a sudden, we felt this rocking and creaking noise, and it felt like we were heading down a hill", said Karnes, adding that several cars had gone off the tracks and passengers kicked out the windows to escape. "They were breathing but not conscious", he said.
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It's believed the passenger train was going at least 128 km/h. She said people driving by also were stopping to help.
A footage of a local TV showed that at least one rail auto fell off a bridge over a traffic-clogged highway.
"We climbed underneath the train as best we could, and there was people, like, with half their bodies pinned who couldn't move and were in a lot of pain".
Konzelman, an Eagle Scout who said he knew a lot about first aid and being a first responder, tried to prepare himself mentally before entering the train cars today, he said today. "Emergency services are on the scene and Amtrak management is responding", it said in an earlier tweet. "I'm not sure what happened at this juncture". "There was some things that I hope nobody ever has to see".
"The motion stopped, and I was able to get out".
President Donald Trump on Monday used a multi-casualty train crash to plug his promise to invest in the nation's infrastructure.