DUPONT, Wash. (CBS News) — An Amtrak train has derailed on an overpass in Washington, and authorities say “injuries and casualties” were reported. At this time, all lanes of traffic remain blocked on Interstate 5.

The Washington State Department of Transportation tweeted a photo of the derailment, urging motorists to avoid the area.

CBS News affiliate KIRO-TV reports 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. in Tacoma, was part of a service that launched Monday morning. 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.

Karnes, who was on board the train when it derailed, said at least seven cars derailed from the tracks. The emergency doors were not functioning correctly, which forced passengers 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. “All of a sudden, we felt this rocking and creaking noise, and it felt like we were heading down a hill. The next thing we know, we’re being slammed into the front of our seats, windows are breaking, we stop, and there’s water gushing out of the train. People were screaming.”

“The tracks for this line were supposed to be upgraded to be able to handle higher speeds,” he added. “I’m not sure what happened at this juncture.”

The cause of the derailment remains under investigation.