DUPONT, Wash. — An Amtrak train making the first-ever run along a faster new route hurtled off an overpass Monday south of Seattle and spilled some of its cars onto the highway below, killing at least six people, authorities said. The death toll was expected to rise.

Seventy-eight passengers and five crew members were aboard when the train moving at more than 80 mph derailed on a route that had raised safety concerns. 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.

A local official had raised concerns about the safety of the new bypass as recently as two weeks ago at a public meeting.

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 train’s 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.

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

Chris Karnes was on the train, three or four cars back from the front. He said the only part of the train remaining on the tracks was the rear locomotive. Several cars were hanging over the overpass.

Daniel Konzelman, 24, 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 he pulled off the freeway and then ran down along the tracks and over the bridge to get to the scene. They saw three cars and a semi-truck on the freeway that had been damaged by the derailment. There were train cars with their roofs ripped off, or that were tipped upside down, on both sides of the track or turned sideways on the bridge.

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.”

They stayed for nearly two hours before hitting the road again.

“I prepared for the worst and hoped for the best. I saw a little bit of both,” he said.

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, on a newly completed bypass, shows “more than ever why our soon to be submitted infrastructure plan must be approved quickly.”

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 train service is jointly owned by the Washington State Department of Transportation and the Oregon Department of Transportation.