DUPONT, Wash. (CBSNewYork/CBS News/AP) — At least three people were confirmed dead after an Amtrak train derailed on an overpass in Washington state Monday, with at least two train cars falling onto the highway below.

Authorities said more than 100 people were also hospitalized after the derailment, which happened on Monday morning. All southbound lanes of traffic remained blocked on Interstate 5 Monday night.

As CBS’2s Tony Aiello reported, work lights illuminated the jumbled mess at the derailment site late Monday night. It was a disastrous day for a maiden voyage of a new Amtrak service.

“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.”

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As CBS2’s Alice Gainer reported, train cars were left scattered like toys after the derailment. Some were overturned, and some were left dangling onto the highway below.

The accident happened near DuPont, Washington, just southwest of Tacoma, on an overpass above busy Interstate 5. It was the inaugural trip of a new high-speed Amtrak train.

Authorities said the derailed train cars struck vehicles on the roadway, injuring multiple motorists.

One train car landed upside down on the roadway.

“Kind of falling over, and the seats in front of me had come dislodged and were swinging around,” said passenger Emma Shafer.

“Right away, you knew that this was not something minor,” said passenger Aleksander Kristiansen. “You felt that right away.”

“Stuff started flying around and just brushed myself off, and was glad I was OK,” said passenger Anthony Raimondi.

A U.S. official who was briefed on the investigation said earlier that at least six people were killed, but the figure was later reduced to three. It wasn’t immediately clear how to reconcile the numbers.

CBS affiliate KIRO-TV, Seattle reported that the injured victims were taken to CHI Franciscan Health St. Joseph Medical Center and Madigan Army Medical Center in Tacoma.

Altogether, at least 50 people were hospitalized, more than a dozen with critical or serious injuries, authorities said.

The train consisted of 14 cars — 12 Talgo passenger cars, each containing 38 seats, which serviced business class, coach cars and bistro service — and two locomotives.

“There were 77 passengers on board, five crew members, five motor vehicles involved on the freeway and two semis,” said Washington State Patrol Trooper Brooke Bova.

“The people that were in all the vehicles — even when you see the pictures, it’s pretty horrific,” added Pierce County, Washington Sheriff’s office spokesman Ed Troyer. “At this point, nobody in any of the vehicles is a fatal.”

First responders rushed to the scene and drivers also did what they could to help.

“I saw smoke,” said driver Trevor Kulvi. “Next thing you know, myself and others are trying to get people medical care when we can.”

Hours after the derailment, officials worked to secure the train cars so they could search them. National Transportation Safety Board investigators also arrived on the scene Monday afternoon to determine exactly why it all happened.

KIRO reported an official who was briefed on the investigation says preliminary signs indicate the Amtrak train may have struck something on the track before derailing.

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.

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 tells the dispatcher, who asks if everyone is OK.

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 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. “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.

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.

Meanwhile, during his speech unveiling his administration’s national security strategy, Mr. Trump commented upon the Amtrak derailment.

“Let me begin by expressing our deepest sympathies and most heartfelt prayers for the victims of the train derailment in Washington state,” Mr. Trump said from the Ronald Reagan building in Washington, D.C. “We are closely monitoring the situation and coordinating with local authorities. It is all the more reason why we must start immediately fixing the infrastructure of the United States.”

But officials said the train derailed on newly-constructed tracks. Amtrak and other agencies spent tens of millions of dollars to upgrade former freight train tracks to accommodate passenger rail moving at 80 mph.

“Absolutely, before they ran this train, they had to run test trains, and the locomotive engineers and the operating crews had to become familiar with this track, so to speak,” said Deborah Hersman of Safety Experts.

Late Monday, NTSB officials said it was too early to determine whether speed played a role.

NTSB investigators said they will look at everything.

“Operations, mechanical, track, signals, human performance and survival factors,” said NTSB member Bella Dinh-Zarr.

The Amtrak Cascades train service is jointly owned by the Washington State Department of Transportation and the Oregon Department of Transportation. Amtrak operates the service for the two states as a contractor and is responsible for day-to-day operations. Amtrak Cascades runs trains from Vancouver, British Columbia, to Eugene, Oregon.

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 was completed in January and February in advance of Monday’s launch, 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.

(© Copyright 2017 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)