PHILADELPHIA (AP) -- Rescue crews searched the mangled wreckage for victims Wednesday as investigators tried to determine why an Amtrak train jumped the tracks in a crash that killed at least six people, injured more than 200 and plunged screaming passengers into darkness and chaos.

An aerial view of the deadly Amtrak train derailment in Philadelphia (AP Photo/Patrick Semansky)

Investigators recovered the train's data recorders and said they expected them to yield crucial information, including how fast the train was going as it rounded a sharp curve and derailed in an old industrial neighborhood not far from the Delaware River shortly after 9 p.m. Tuesday.

"It's a devastating scene. There are many first responders out there. They are working. They are examining the equipment, seeing if there are any more people in the rail cars," Robert Sumwalt of the National Transportation Safety Board said.

Mayor Michael Nutter said some people remained unaccounted for, raising fears the death toll could rise, though he cautioned that some passengers listed on the Amtrak manifest might not have boarded the train, while others might not have checked in with authorities.

The dead included a midshipman at the U.S. Naval Academy.

"We are heartbroken by what has happened here," Nutter said.

The train was en route from Washington to New York with 238 passengers and five crew members listed aboard when it lurched to the side and flew off the tracks at a notorious curve not far from the scene of one of the nation's deadliest train wrecks more than 70 years ago.

Passengers scrambled through the windows of toppled cars to escape. One of the seven cars was severely mangled. Hospitals treated more than 200 people for injuries that included burns and broken bones. At least 10 were hospitalized in critical condition.

Emergency personnel gather near the scene of a deadly train derailment in Philadelphia (AP Photo/Mel Evans)

New Jersey Gov. Chris Christie asked  Chief Counsel Chris Porrino to have New Jersey emergency management to reach out to Philadelphia and offer help "They told us, at the time, they didn't need help. They thought they had the situation under control," said the governor in a statement.

"As you guys know, I ride that train route often. And have for the last thirteen years, so it's really disconcerting. And my thoughts go out to the families of those who have been lost and injured," said the governor, who started his day in New Hampshire following a town hall meeting.  "But, I'm fascinated to know what happened since me and a lot of my staff ride that train on a regular basis. So, hopefully we'll get to the bottom of why it happened and try to make sure we try to do what we need to do to prevent it again."

"Along with Americans across our country, Michelle and I were shocked and deeply saddened to hear of the derailment aboard Amtrak Train 188. Our thoughts and prayers go out to the families and friends of those we lost last night, and to the many passengers who today begin their long road to recovery,"  said President Obama in a statement, offering praise for rescue crews and first responders. "Philadelphia is known as the city of brotherly love – a city of neighborhoods and neighbors – and that spirit of loving-kindness was reaffirmed last night, as hundreds of first responders and passengers lent a hand to their fellow human beings in need. "

[Amtrak has established an "Incident Hotline" at 800-523-9101 for those seeking information about family and friends who may have been on the train.]

The accident closed the nation's busiest rail corridor between New York and Washington - snarling the morning commute and forcing thousands of travelers to find some other way to reach their destination - as federal investigators arrived to begin examining the twisted wreckage, the tracks and the signals.

Investigators and first responders work near the wreckage of an Amtrak passenger train in Philadelphia (Win McNamee/Getty Images)

The conductor survived and was expected to give a statement to police. The train also had a video camera in its front end that could yield clues to what happened, Sumwalt said.

Passenger Jillian Jorgensen, 27, was seated in the quiet car - the second passenger car - and said the train was going "fast enough for me to be worried" when it began to lurch to the right.

The train derailed, the lights went out and Jorgensen was thrown from her seat. She said she "flew across the train" and landed under some seats that had apparently broken loose from the floor.

Jorgensen, a reporter for The New York Observer who lives in Jersey City, New Jersey, said she wriggled free as fellow passengers screamed. She saw one man lying still, his face covered in blood, and a woman with a broken leg.

She climbed out an emergency exit window, and a firefighter helped her down a ladder to safety.

"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 U.S. Naval Academy did not immediately release the name of the midshipman killed in the crash but said the student was on leave and heading home.

All seven train cars, including the engine, were in "various stages of disarray," Nutter said. He said there were cars that were "completely overturned, on their side, ripped apart."

Emergency personnel working at the site of a train accident in Philadelphia. (AP Photo / Joseph Kaczmarek)

An AP manager, Paul Cheung, was on the train and said he was watching a video on his laptop when "the train started to decelerate, like someone had slammed the brake."

"Then suddenly you could see everything starting to shake," he said. "You could see people's stuff flying over me."

Cheung said another passenger urged him to escape from the back of his car, which he did. He said he saw passengers trying to get out through the windows of cars tipped on their sides.

"The front of the train is really mangled," he said. "It's a complete wreck. The whole thing is like a pile of metal."

Gaby Rudy, an 18-year-old from Livingston, New Jersey, was headed home from George Washington University. She said she was nearly asleep when she suddenly felt the train "fall off the track."

The next few minutes were filled with broken glass and smoke, said Rudy, who suffered minor injuries. "They told us we had to run away from the train in case another train came," she said.

Another passenger, Daniel Wetrin, was among more than a dozen people taken to a nearby elementary school.

"I think the fact that I walked off kind of made it even more surreal because a lot of people didn't walk off," he said. "I walked off as if, like, I was in a movie. There were people standing around, people with bloody faces. There were people, chairs, tables mangled about in the compartment ... power cables all buckled down as you stepped off the train."

Several people, including one man complaining of neck pain, were rolled away on stretchers. Others wobbled as they walked away or were put on buses. An elderly woman was given oxygen.

The area where the wreck happened is known as Frankford Junction, situated in a neighborhood of warehouses, industrial buildings and homes.

It is not far from the site of the 1943 derailment of the Congressional Limited, from Washington to New York, which killed 79 people.

Amtrak's busy Northeast Corridor between Washington and Boston serves 11.6 million passengers a year. More than 2,200 trains running on at least some portion of the Washington-to-Boston tracks each day.

The mayor, citing the mangled tracks and downed wires, said: "There's no circumstance under which there would be any Amtrak service this week through Philadelphia."

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