A Washington-New York Amtrak train service has derailed in Philadelphia killing at least five people and injuring dozens of others, six of whom are in a critical condition.

Ten carriages of the passenger train went off the tracks in Port Richmond, a working class suburb of Philadelphia, after leaving the city's main station on Tuesday evening (12 May). More than 240 people were on board Train 188. It is not known what caused the derailment.

Emergency crews and firefighters were struggling to free people trapped in the train. Most passengers were either from Washington, New Jersey or New York according to authorities.

"It is a devastating scene," Philadelphia Mayor Michael Nutter told reporters. "Never seen anything like this in my life."

"We walked the entire length of the train area. The engine [is] completely separated from the rest of the train and one of the cars is perpendicular to the rest of the cars. It's unbelievable."

Initial reports indicated that the train derailed as it entered a curve.

An AP manager, Paul Cheung, was on the train and described the scene:

"The train started to decelerate like someone had slammed the brake.

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

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