A New York passenger train that derailed on Monday morning killing at least four was traveling nearly three times faster than the speed limit for the curved section of track, officials have said.
The train was traveling at 82mph before entering the 30-mile-per-hour curve.
A spokesman for the city's fire services said 11 of the 63 people injured in Sunday's accident were in critical condition while six were in serious condition with non-life threatening injuries.
The recorders showed the train's brakes were applied "very late in the game," National Transportation Safety Board member Earl Weener told reporters.
The train hurtled off the tracks in the Bronx at 7:20am near the Spuyten Duyvil station.
At least 130 firefighters are on the scene, the fire department said.
The train, headed south toward Manhattan's Grand Central Terminal, was about half full at the time of the crash with about 150 passengers and was not scheduled to stop at the Spuyten Duyvil station, said the state's Metropolitan Transportation Authority (MTA), parent company of Metro North.
"On a workday, fully occupied, it would have been a tremendous disaster," Salvatore Joseph Cassano, New York City Fire Commissioner, told reporters at the scene.
After touring the site, New York Governor Andrew Cuomo told CNN: "That is a dangerous area on the track just by design."
He added: "The trains are going about 70 miles per hour (112 kph) coming down the straight part of the track. They slow to about 30 miles per hour (48 kph) to make that sharp curve ... where the Hudson River meets the Harlem River and that is a difficult area of the track."
The National Transportation Safety Board has begun its investigation and Cuomo said it appeared that all passengers had been accounted for.
The MTA said four or five carriages on the seven-carriage train derailed about 100 yards north of the station on a curved section of the track. But the MTA said none of the carriages entered the Hudson or Harlem rivers, which are adjacent.
Edwin Valero, who was in an apartment building above the accident scene when the train derailed, told the Associated Press news agency that none of the carriages went into a nearby body of water, but at least one ended up a few feet from the edge.
Witness Rebecca Schwartz told AP that she was at a nearby park when the accident occurred. She said she did not see or hear the derailment but looked across the water when she heard emergency vehicle sirens.
She said numerous emergency vehicles had responded to the scene.