This photo provided by Washington State Patrol shows an Amtrak train that derailed south of Seattle on Monday, Dec. 18, 2017. Authorities reported “injuries and casualties.” The train derailed about 40 miles (64 kilometers) south of Seattle before 8 a.m., spilling at least one train car on to busy Interstate 5. (Washington State Patrol via AP)

DUPONT, Wash. (AP) — An Amtrak train making the first-ever run along a faster new route hurtled off an overpass at an estimated 80 mph Monday south of Seattle and spilled some of its cars onto the highway below, killing at least six people, authorities said.

Seventy-seven passengers and five crew members were aboard when the train derailed. At least 50 people were hospitalized, more than a dozen with critical or serious injuries, authorities said.

An official briefed on the investigation told The Associated Press that preliminary signs indicate that Train 501 may have struck something before going off the track about 40 miles (64 kilometers) south of Seattle. The official was not authorized to discuss the investigation publicly and spoke on the condition of anonymity.

The Pierce County Sheriff’s Office said several vehicles on Interstate 5 were struck by falling train cars and multiple motorists were injured. No fatalities of motorists were reported.

In a radio transmission immediately after the accident, the conductor can be heard saying the train was coming around a corner and was crossing a bridge that passed over Interstate 5 when it derailed. Dispatch audio also indicated that the engineer survived with bleeding from the head and both eyes swollen shut.

“I’m still figuring that out. We’ve got cars everywhere and down onto the highway,” he tells the dispatcher, who asks if everyone is OK.

Aleksander Kristiansen, a 24-year-old exchange student at the University of Washington from Copenhagen, was going to Portland to visit the city for the day.

“I was just coming out of the bathroom when the accident happened. My car just started shaking really, really badly. Things were falling off the shelf. Right away, you knew that this was not something minor,” he said.

The back of his train car was wide open because it had separated from the rest of the train, so he and others were able to jump out to safety. He was at about the middle of the train, either the sixth or seventh car, he said, and was “one of the lucky ones.”

Daniella Fenelon, a 19-year-old from Southern California, was on the train taking a cross-country trip as part of her winter break. She said she was asleep when the accident happened.

“Suddenly there was just a jolt, and I didn’t know what was happening,” Fenelon said. She slammed into the seat area in front of her, and the windows exploded, said Fenelon, who was treated and released from a hospital with a possible concussion.

Dr. Nathan Selden, a neurosurgeon at the Oregon Health & Science University in Portland, said he and his son drove through the accident scene while traveling north to visit Seattle. The doctor asked if he could help and was ushered to a medical triage tent in the highway median.

The most seriously injured had already been whisked away, but the patients he helped appeared to have open head wounds and skull, pelvic or leg fractures, as well as small cuts and neck sprains, he said.

He called it a miracle that an infant child he saw from the scene appeared completely unharmed.

President Donald Trump used the deadly derailment to call for more infrastructure spending in a tweet sent about three hours after the accident. He said the wreck shows “more than ever why our soon to be submitted infrastructure plan must be approved quickly.” The accident happened on a newly completed bypass.

The train was making the inaugural run on the new route as part of a $180.7 million 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.

The Amtrak Cascades service that runs from Vancouver, British Columbia, to Eugene, Oregon, is jointly owned by the Washington and Oregon transportation departments. Amtrak operates the service for the two states as a contractor and is responsible for day-to-day operations.

The Amtrak schedule called for the train to leave Seattle around 6 a.m. and arrive in Portland about 3 1/2 hours later.

Monday marked the first public use of the new bypass built on an existing inland rail line that runs along Interstate 5 from Tacoma to DuPont, near where Train 501 derailed. Track testing began in January and February in advance of Monday’s launch and continued through at least July, according to the Washington State Department of Transportation.

The tracks, known as the Point Defiance Bypass, are owned by Sound Transit, the transit agency serving the Seattle area. They were previously owned by BNSF and were used for occasional freight and military transport.

The mayor of Lakewood, Washington, a city along the new route, predicted a deadly crash — but one involving a fast-moving train hitting a car or pedestrian at a grade-crossing, not a train tumbling off an overpass. At a recent public meeting, he called on state planners to build overpass-like rail structures instead of having trains cross busy streets.

The National Transportation Safety Board said a team of investigators was on its way to the scene from Washington, D.C.

The train was going 81.1 mph moments before the derailment, according to transitdocs.com, a website that maps Amtrak train locations and speeds using data from the railroad’s train tracker app.

The maximum speed along the stretch of track is 79 mph, according to information about the route posted online by the Washington State Department of Transportation.

All southbound lanes of I-5 were closed south of Joint Base Lewis-McChord, and motorists were being warned to avoid the area.

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Flaccus reported from Portland. Associated Press staffers Manuel Valdes in Dupont; Sally Ho and Phuong Le in Seattle; Michael Sisak in Philadelphia and Michael Balsamo in Los Angeles contributed to this report.

Please be advised of a massive incident involving a train derailing on the Mounts Rd overpass on I5. The train is currently blocking I5. Please avoid this area and Nisqually Valley. Be patient with traffic and emergency vehicles in the area. WSP is investigating this incident. pic.twitter.com/lFrXPQDSA1

— Thurston Co. Sheriff (@ThurstonSheriff) December 18, 2017