The train derailment accident on Monday has left 91 people dead and more than 450 others injured, police said Wednesday.

The death toll is feared to breach 100 as about a dozen of passengers remain trapped in the first two cars and showed no sign of living, according to Japanese media reports.

The train jumped the track right after morning rush hour in Amagasaki, Hyogo Prefecture, and punched into a nearby apartment building.

The cause of the accident remains undetermined, while the focus is now on speeding.

The train was running over 100 kilometers per hour (kph) when the derailment occurred at a curve, much faster than the 70 kph upper limit, the reports quoted police as saying.

Investigators also are looking into marks on the track, suspecting that the train might run over stones possibly placed by someone on the rail.

The two front cars were badly damaged after ramming into the building, making it greatly difficult for rescue workers to reach the remaining passengers.

Local police determined the train's speed after having found its speed recording device, the reports said.

Many survivors also said that they felt the train was running unusually fast.

The train was one and a half minutes behind schedule when it started at the last station. The 23-year-old driver missed the proper stop position by 40 meters and had to back up, the West Japan Railway Co. said on Tuesday. The company said that the conductor of the train conspired with the driver to report to the command center that the overrun was only eight meters.

The train theoretically would derail if its speed exceeded 130 kph but it was designed to have a top speed of 120 kph.

The death toll made itself the most serious in Japan since May 14, 1991, when 42 were killed and 527 injured in a collision of two trains in west Japan.