"This was an absolute disastrous mess,"

"All of a sudden it felt like the brakes were hit hard and then our car," said Michael Black, one of the passengers. "We were third from the last, just slowly started going over to the side. I tried to just brace my arm against it and then just got off."

Daniel Hernandez, who lives close to the tracks, heard the derailment.

"It sounded like a bunch of shopping carts crashing into each other," he said.

Hernandez says the crashing sound lasted a few seconds and he heard chaos and screaming.

Mayor Michael Nutter confirmed at least five people were killed in the derailment during a news conference late Tuesday.

"This was an absolute disastrous mess," Nutter said. "I have never seen anything like it in my life. Many of these folks are not from Philadelphia."

Nutter, who said the incident was a "Level 3 mass casualty event," did not speak on a possible cause.

"We do not know what happened here," he said. "We're not going to try to speculate about that."

Governor Tom Wolf arrived at the scene and spoke with Mayor Nutter during another press conference shortly after 1 a.m. Wednesday. Wolf said his thoughts and prayers are with the victims of the crash and all those affected.

Officials have not yet revealed the identity of the deceased victims.

"I've never seen anything so devastating," said Philadelphia Fire Department Deputy Commissioner Jesse Wilson. "They're in pretty bad shape. You can see that they're completely, completely derailed from the track. They've been destroyed completely. The aluminum shell has been destroyed and they've been overturned completely."

Officials say over 140 people were hospitalized and at least six of them are in critical condition. Victims were taken to Temple University Hospital, Aria Health-Frankford, Hahnemann University Hospital and the Albert Einstein Medical Center.

Jefferson University Hospital treated 26 patients, the majority of which had minor injuries, according to a spokesperson.

A spokesperson at Temple University Hospital says they treated at least 36 people who are in various conditions.

An Aria Health spokeswoman says 26 patients were treated at its Frankford location while 50 were brought to its Torresdale hospital.

Hahnemann University Hospital treated about 25 patients with mostly minor injuries and a few traumas according to a spokesman.

Finally, Albert Einstein Medical Center treated 10 patients.

The incident required a 4-alarm response, including 120 firefighters and 200 police officers. An emergency response staging area was established at Frankford and Castor streets.

Officials say they don't believe the incident was an act of terror and preliminary information indicates it was an accident.

The National Transportation Safety Board has sent a go-team to investigate the derailment. Members of that team arrived early wednesday morning. NTSB investigator Mike Flanigon is leading the team as investigator-in-charge. NTSB Board Member Robert Sumwalt is accompanying the team and will serve as the main spokesman during the on-scene phase of the investigation.

The derailment occurred at almost the exact same location of another deadly derailment 71 years ago. On Sept. 6, 1943, a Congressional Limited careened off the tracks with 541 passengers on-board, including many service members on leave. Seventy-nine passengers were killed and 117 were injured.

Yameen Allworld, a Philadelphia music producer who has worked with the Roots, was on the train and posted a video on Instagram. In the video passengers could be heard crying and crawling through the sideways car.

Janelle Richards, a producer for NBC Nightly News, was another passenger on the train. Richards says she heard a loud crash around 9:20 p.m. She also said people flew up in the air and there was a lot of "jerking back and forth" and "a lot of smoke."