Daylight revealed mangled train cars Wednesday after an Amtrak passenger train derailed and overturned in Philadelphia, killing at least six people and injuring dozens of others, some of whom scrambled through the windows to escape.

The busiest rail corridor in the U.S., between New York and Washington remained closed as investigators looked for what went wrong in Tuesday night's crash. More than 140 people were hospitalized, some critically injured, many with burns or fractures.

Temple University Hospital's Dr. Herbert Cushing announced the latest death, saying the sixth person died overnight from a chest injury.

Mayor Michael Nutter overnight said not all of the people on the train had been accounted for. Amtrak said the train was carrying 238 passengers and five crew members.

"It is an absolute disastrous mess," Nutter said. "I've never seen anything like this in my life."

He said all seven train cars, including the engine, were in "various stages of disarray." He said there were cars that were "completely overturned, on their side, ripped apart." The engine was completely separated from the rest of the train, and one of the cars was perpendicular to the rest of the cars, he said.

The train, traveling from Washington, D.C. to New York City, was going into a turn when it started to shake before coming to a sudden stop.

Passenger Jillian Jorgensen, 27, said the train was going "fast enough for me to be worried" when it began a hard bank to the right. The train derailed, and the lights went out. Jorgensen said she "flew across the train" and landed underneath some seats.

Jorgensen said she managed to wriggle free as passengers screamed. She saw one man lying still, his face covered in blood, and a woman with a broken leg.

"It was terrifying and awful, and as it was happening it just did not feel like the kind of thing you could walk away from, so I feel very lucky," Jorgensen said in an email to The Associated Press. "The scene in the car I was in was total disarray and people were clearly in a great deal of pain."

The area where the derailment occurred is not far from the scene of one of the deadliest U.S. train accidents: the 1943 derailment of The Congressional Limited, from Washington to New York, which killed 79 people.

Amtrak said rail service on the Northeast Corridor between New York and Philadelphia had been stopped.

Former U.S. Rep. Patrick Murphy was on the train and tweeted photos of firefighters helping other people in the wreckage.

"Pray for those injured," he said.