Philadelphia (US): A US passenger train was traveling at more than 100 miles per hour -- twice the speed limit -- when it derailed in Philadelphia, investigators said Wednesday, as the death toll from the crash rose to seven.

The National Transportation Safety Board's first assessment of the data came as experts combed through the twisted train cars for more clues about how Tuesday night's wreck occurred.

More than 200 people, including from India, were injured in the crash, which took place along the busy northeast US rail corridor linking Washington and New York, one of the most traveled in the Amtrak network.

Officials warned some of the 243 passengers and crew believed to have been on the train -- many of whom limped away from the wreck bloodied and dazed -- had not yet been accounted for, meaning the death toll could still rise.

The train's "black box" was recovered and sent for analysis, hopefully yielding key information about what went wrong.

"NTSB confirms preliminary data shows #Amtrak train speed exceeded 100 mph prior to derailment. Further calibrations are being conducted," the agency said on Twitter.

A spokesman for the US Federal Railroad Administration told AFP the speed limit in the curve was just 50 miles (80 kilometers) per hour. The NTSB said more information would be given at a press
conference at 5:00 pm (2100 GMT).

"We'll get to the bottom of it and figure out what happened, why it happened, but that will take some time," Philadelphia Mayor Michael Nutter told reporters. Sam Phillips, the city's director of emergency
management, said the city's hospitals had treated "over 200 patients last night and this morning."

Herbert Cushing, the chief medical officer at Temple University Hospital, said some of those most seriously injured suffered rib fractures or collapsed lungs. Some of the victims hailed from Spain, Belgium, Germany and India.

Reportedly among the dead were a staffer for the Associated Press and a midshipman at the US Naval Academy, according to the AP and the Washington Post. Witnesses who had been traveling aboard Amtrak Train 188 described scenes of panic and chaos, as cars tumbled over, sending passengers banging into one another and luggage flying.