An Amtrak train on its inaugural run derailed Monday morning while barrelling across an overpass in Washington state, killing at least three passengers and severely injuring others as it crashed onto a highway below, officials said.

Stunning photos show the wreckage of Amtrak 501 dangling and crumpled on I-5 near Lacey, just east of the state capital, Olympia.

A spokesman for the Pierce County Sheriff’s Office said those killed were all on the train and the injured included motorists whose vehicles were struck by the out-of-control rolling stock, according to the Seattle Times.

About a dozen victims, including three in critical condition, were being treated at Providence St. Peter Hospital in Olympia, a spokesman told the paper, while others had to be rushed to Tacoma, more than 30 miles away.

“Because traffic is so backed up, a lot of the EMS responders are taking patients to hospitals in Tacoma,” spokesman Chris Thomas said.

Some of the train’s passengers were trapped inside, according to KIRO 7 TV, and a state police official told reporters that a “rescue operation” was still underway shortly before 1 p.m. Eastern time, more than two hours after the crash.

There were 78 passengers and five crew members on board the train, Amtrak said.

The cause of the derailment, which occurred some time before 7:45 a.m. local time, is under investigation.

Passenger Chris Karnes described the horror that unfolded when the train left the rails.

“We had just passed the city of DuPont and it seemed like we were going around a curve,” Karnes told CBS News.

“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.”

Karnes said that at least seven cars derailed, and that passengers had to kick out the train’s windows to escape when the emergency doors failed to open.

“The tracks for this line were supposed to be upgraded to be able to handle higher speeds,” Karnes said.

“I’m not sure what happened at this juncture.”

The train was headed southbound from Seattle, Washington, to Portland, Oregon, on the first trip of a new “Amtrak Cascades” daily route that went into service at 6 a.m. Monday.

The new route was established as part of a $181 million project that included a new Amtrak station in Tacoma and installation of high-speed rails known as the “Point Defiance Bypass,” according to the Seattle Times.

The new tracks run near the US Army’s Joint Base Lewis-McChord, which last week posted an online warning that “trains traveling about 80 miles per hour” would be passing through local railroad crossings 14 or more times a day.