DUPONT, Wash. -- An Amtrak train derailed on an overpass in Washington state Monday morning, with some of the 14 train cars careening onto vehicles on a highway below. The crash resulted in at least three confirmed fatalities and numerous injuries, and authorities are still combing through the wreckage to find victims.
At this time, all southbound lanes of traffic remain closed on Interstate 5.
"Today's tragic incident in Pierce County is a serious and ongoing emergency," Washington Gov. Jay Inslee wrote 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."
The Washington State Department of Transportation tweeted a photo of the derailment, urging motorists to avoid the area.
All SB lanes of I-5 blocked near Mounts Road in Pierce County due to derailed train car. Avoid area! pic.twitter.com/SBH7dCc6yg
— WSDOT Tacoma Traffic (@wsdot_tacoma) December 18, 2017
Authorities say the derailed train cars struck five motor vehicles and two semi-trucks on the highway.
CBS News affiliate KIRO-TV reports an official who was briefed on the investigation said preliminary signs indicate the Amtrak train may have struck something on the track before derailing, but it was too soon to determine the cause of the accident.
First responders are treating the derailment as a mass casualty incident. Authorities have not yet provided details on injuries.
"Emergency crews are on the scene and the Amtrak Management is responding," an Amtrak spokesperson said in a statement. "Some injuries are reported. Service between Seattle and Portland is suspended for the time being."
Amtrak train 501, which departed shortly before 8 a.m. local time from Tacoma, was part of a new high-speed service that launched Monday morning. The train is able to carry up to 250 people, but Amtrak said there were approximately 80 passengers, five Amtrak crew members and one technician from Talgo, the train car manufacturer, on board at the time.
The Cascades service from Seattle to Portland was supposed to be rated for a maximum speed of 79 mph for the section where it derailed in DuPont, according to passenger Chris Karnes. KIRO-TV reports the train was traveling at 81 mph moments before the derailment.
Karnes, who was on board the train when it derailed, said the emergency doors on the train were not functioning correctly after the crash and passengers had to kick out train windows to exit.
"We had just passed the city of DuPont and it seemed like we were going around a curve," Karnes said. "And all of a sudden, we felt this rocking and creaking noise, and then all of a sudden it felt like we were heading down a hill, and the next thing that we know, we're being slammed into the front of our seats, and the windows are breaking, and then we stop, and there's water that's gushing out of the top of the train and all the lights go out and people are screaming."
"The tracks for this line were supposed to be upgraded to be able to handle higher speeds," he added. "So, I'm not sure what happened at this juncture."
CBS News correspondent Kris Van Cleave reports the train tracks themselves are not owned by Amtrak; they're maintained by a freight railroad. "The tracks, known as the Point Defiance Bypass, are owned by Sound Transit," the Washington State Department of Transportation wrote in a statement. "The tracks were previously owned by BNSF and were used for occasional freight and military transport."
Motorist Greg Mukai, who witnessed the derailment from the highway, described the incident as "really scary stuff."
"We suddenly had to go from our 60 mph down to zero as fast as possible," he said. "We were all avoiding one another to try and avoid a collision there. We saw smoke and the passenger train hanging from the overpass and on the freeway."
A photo taken by a Washington state trooper showed one car of the train smashed upside down on the highway and another hanging off the bridge above it.
The cause of the derailment remains under investigation. An NTSB team is being sent from Washington, D.C., to investigate the incident.