An Amtrak train making its first run along a faster new route hurtled off an overpass south of Seattle on Monday and spilled some of its cars onto the highway below, killing at least three people, fire officials said.

The derailment occurred about 64 kilometres south of Seattle just before 7:40 a.m. PT.

There were 80 passengers and five on duty crew when the train derailed and pulled 13 cars off the tracks. Authorities said there were three confirmed deaths. More than 70 people were taken for medical care — including 10 with serious injuries.

Authorities said all the train cars have been searched but they didn't know if everyone was accounted for. CBC's Briar Stewart reported that fire crews said they had to use saws to get through some of the wreckage.

By evening, National Transportation Safety Board investigators were at the scene, tasked with trying to learn what caused the derailment, and cranes had been brought in to stabilize the train cars so the crash scene could be cleared. 

Passengers pinned under wreckage

Daniel Konzelman, 24, said he was driving parallel to the train on his way to work as an accountant in Olympia. He was about 30 seconds ahead of the train on the freeway when he saw it derail.

Konzelman, who was driving with a friend, said they pulled off the freeway and then ran down along the tracks and over the bridge to get to the scene. 

They climbed into train cars and found people hurt — some pinned underneath the train, others who appeared to be dead, he said.

 If they were mobile and seemed stable, he helped them climb out. If they appeared seriously hurt, he tried to comfort them by talking to them.

"I just wanted to help people because I would want people to help me," he said. "I'm an Eagle Scout. I have a lot of first-aid training and emergency response training."

'A very scary moment'

Greg Mukai told CBC News that first responders arrived at the scene quickly and that military personnel from the nearby Joint Base Lewis-McChord also descended on the scene to offer help.

"All of the traffic around me, including myself, we had to come to a sudden and complete stop — to the point that cars were darting to the sides of the freeway to avoid colliding with one another," he said.

"As soon as we came to a stop, relieved we didn't run into anybody, we looked up to see why the traffic had stopped and I was about 50 yards away from the result, which was the train had derailed, come off of the overpass and collided onto the highway.

"Cars were impacted, and it was a very scary moment."

'Cars everywhere'

A member of the train's crew told an emergency dispatcher that the train came around a corner before the bridge and then "we went on the ground."

After the dispatcher asked whether everyone was OK, the crew member replied, "I am still figuring that out. We got cars everywhere and down onto the highway."

The dispatcher also asked for the driver's location, and he responded, "As soon as I know exactly where all of my train is, I'll let you know."

Amtrak crew member's call to dispatch0:47

'Serious and ongoing emergency'

Washington Gov. Jay Inslee offered condolences to the victims and declared a state of emergency.

"Today's tragic incident in Pierce County is a serious and ongoing emergency," Inslee said in a statement. "Trudi and I are holding in our hearts everyone on board, and are praying for the many injured. They are our top priority, and I know first responders are doing everything to ensure everyone has the care they need."

Inslee said officials were working on opening alternate routes to help travellers.

Amtrak revised the numbers of people on board throughout the day. As of Monday evening, the company said there were "approximately 80 passengers and five crew members on board."

New route 

The Amtrak schedule called for the train to leave Seattle around 6 a.m. and arrive in Portland about 3½ hours later.

The train was making the inaugural run on the new route as part of a $180.7-million US project designed to speed up service by removing passenger trains from a route along Puget Sound that's bogged down by curves, single-track tunnels and freight traffic.

Track testing was completed in January and February in advance of Monday's launch, according to the Washington State Department of Transportation.

APTOPIX Train Derailment Washington State

Cars from an Amtrak train lay spilled onto Interstate 5 below alongside smashed vehicles as some train cars remain on the tracks above Monday in DuPont, Wash. (Elaine Thompson/Associated Press)

Don Anderson, mayor of Lakewood, Wash., a city along the new route, predicted a deadly crash, albeit one involving a fast-moving train hitting a car or pedestrian at a grade-crossing. At a recent public meeting, he called on state planners to build overpass-like rail structures instead of having trains cross busy streets.

According to Transitdocs.com, a website that maps Amtrak train locations and speeds using data from the railroad's train tracker app, Train 501 was going 130 km/h moments before the derailment.

Amtrak's statement said individuals with questions about their friends and family on Train 501 should call 1-800-523-9101.

President Donald Trump on Twitter said his thoughts and prayers were with anyone affected by the incident, several minutes after a first tweet that said the derailment "shows more than ever why our soon to be submitted infrastructure plan must be approved quickly."

APTOPIX Train Derailment Washington State

Cars from an Amtrak train that derailed lie spilled onto Interstate 5 on Monday in DuPont, Wash. (Bettina Hansen/The Seattle Times via AP)

With files from CBC News and Reuters