The engineer of a US passenger train that was travelling at more than 160km/h - twice the approved speed - slammed on the emergency brakes just before a deadly derailment in Philadelphia, investigators have said.
The driver engaged in a "full emergency brake application" moments before the derailment, but the train speed only decreased by a few miles per hour”, Robert Sumwalt of the National Transportation Safety Board told reporters.
The preliminary data came from the so-called ‘black box’ recovered from the wreckage after Tuesday night's crash of Amtrak Train 188, which was headed from Washington to New York.
At least seven people were killed and more than 200 others injured.
The emergency brakes only slowed the train speed from 170km/h to 164km/h, Mr Sumwalt said, noting: "It takes a long time and distance to decelerate a train."
He said a speed control system in place along parts of Amtrak's Northeast Corridor between Washington and New York was not yet in place on that particular section of tracks.
"We feel that had such a system been installed in this section of track, this accident would not have occurred," he said.
National Transportation Safety Board investigation team is expected to be on the scene for about a week.
The train was travelling from Washington DC to New York City with 243 people on board, including five crew, when it derailed.
Officials reiterated that not all of the people on board had been accounted for, without offering a figure.
They added that some people may simply have left the scene uninjured.
Six other people are in a critical condition and another 52 have injuries described as 'less critical'. 
The cause of the crash is not yet known.
Several Philadelphia-area hospitals collectively reported treating more than 100 patients from the wreck.
"It's an absolute disastrous mess," Mr Nutter said. "I've never seen anything like this in my life."
Philadelphia Police Commissioner Charles Ramsey told reporters that rescue personnel were using "a large number of tourniquets" in treating the injured.
At least one area hospital spokeswoman said many of their patients were suffering from lacerations.
Seven carriages, including the engine, left the tracks, according to the mayor.
CNN quoted the Federal Bureau of Investigation as saying there was no indication that terrorism may have been a factor in the derailment.
Three law enforcement officials contacted by Reuters news agency also said they have not encountered anything suspicious. The weather was fair at the time of the crash.
"We do not know what happened here. We do not know why this happened," Mr Nutter told reporters.
He later told CNN there was no indication that the train derailed due to a collision with another train.
He also said the train derailed on a curved stretch of track, adding: "We have no idea what kind of speed we're talking about."
A spokesman for the Department of Foreign Affairs said at this stage there is no indication that any Irish people were involved in the train derailment.
