Washington, May 14 (IANS): An Amtrak passenger train that derailed in the US city of Philadelphia killing seven people and injuring over 200 others, was traveling twice as fast than the permitted speed limit, the National Transportation Safety Board (NTSB) said.

NTSB spokesman Robert Sumwalt on Wednesday said that the train was travelling at 106 miles per hour (mph), while the speed limit for the curve is 50 mph. The emergency brakes slowed the train from 106 mph to 102 mph before "the entire train derailed", Xinhua news agency reported on Thursday.

The Amtrak Northeast Regional Train 188 was carrying 238 passengers and five crew members when it derailed in the Port Richmond neighbourhood just minutes after making a scheduled stop at Philadelphia's 30th Street station.

The black box data recorders will be sent to Washington DC for assessment, Sumwalt said adding his team would also examine other details, such as the condition of the track and the train, how signals operated and "human performance".

Philadelphia Mayor Michael Nutter Wednesday confirmed the toll rose to seven, as emergency crews continued to search for more survivors.

"It is an absolute, disastrous mess," Nutter said.

The rescue operation is still under way.

The Federal Bureau of Investigation (FBI) said that so far there was nothing to indicate the incident was an act of terrorism.