Update -- A sixth person has died as a result of the Amtrak train crash in Philadelphia, a doctor at Temple University Hospital said Wednesday morning.
Eight passengers remain in critical condition at Temple.
Many passengers were injured when other passengers and objects flew into them, a hospital official said.
PHILADELPHIA -- Armed with flashlights, firefighters went from car to car early Wednesday morning, looking for passengers inside an Amtrak train that derailed and tipped over in Philadelphia -- killing at least five.
Another 136 were taken to various hospitals, including six in critical condition, authorities said.
"It is an absolute, disastrous mess," Philadelphia Mayor Michael Nutter of the crash site. "I've never seen anything like this in my life."
The Amtrak Northeast Regional Train 188 was traveling from Washington to New York when it derailed in the Port Richmond neighborhood of Philadelphia about 9:30 p.m. Tuesday. The impact tore cars apart and left the engine a mangled mess.
The northeast corridor, which spans from Washington to Boston, is the busiest passenger line in the country, and the train was carrying 238 passengers and 5 crew members.
The cause wasn't immediately known.
"We do not know what happened here. We do not know why it happened," Nutter said. There was no indication the derailment was a result of an impact with another train, he said.
So far, there's nothing to indicate the incident was an act of terrorism.
Early Wednesday morning, investigators in orange vests walked up and down the track, especially near a part where it curves.
The area of the crash is known as Frankford Junction. In 1943, it was the site of one of the nation's deadliest train accidents when The Congressional Limited crashed, killing 79 people.
"Until the second of impact, everything was normal," passenger Daniel Wetrin told CNN. "Then it was just chaos."
The moment of impact
Jeremy Wladis was in the very last car, eating.
"The next thing you know, the train starts doing funny things, and it gradually starts getting worse and worse," he said.
Then, things started flying -- phones, laptops. "Then people."
"There were two people in the luggage rack above my head. Two women, catapulted [there]."
Firefighters arrived to find seven cars and the train's engine either turned over or upside down. Most of the passengers were able to escape, climbing out of windows to safety. Crews had to cut through the cars to get to others.
'Please make it stop'
Janna D'Ambrisi was in the second-to-last car, reading her book when she felt the jolt.
"Suddenly it felt like we were going a little too fast around a curve," she said.
The car she was in started to tip and she was thrown onto another girl.
"People started to fall on us," D'Ambrisi said.
"I just held on to her leg and sort of bowed my head and I was kind of praying, 'Please make it stop.'"
Fortunately, her car didn't tip over and she was able to make it out safely.
At a news conference around 1 a.m., Mayor Nutter said he couldn't say whether all the passengers had been accounted Officials with the National Transportation Safety Board will arrive at the scene in the morning, and the investigation into what happened will begin.
The deadliest accident in Amtrak's history took place in September 1993, when a tugboat smashed into a river bridge, causing it to collapse as an Amtrak train was passing over. The accident in Mobile, Alabama, killed 47 people.
Amtrak shut down rail service between Philadelphia and New York City Tuesday night. It set up a special number for those seeking information on friends and family aboard the train: 1-800-523-9101.