AMAGASAKI, Japan (AP) -- A packed commuter train jumped the tracks in western Japan on Monday and hurtled into an apartment complex, killing 52 people and injuring more than 417 others in the deadliest Japanese rail accident in four decades.
Investigators focused on whether excessive speed or the actions of the inexperienced, 23-year-old driver caused the crash in an urban area near Amagasaki, about 250 miles west of Tokyo.
Several passengers speculated that the driver may have been speeding to make up for lost time after overshooting the previous station, forcing him to back up to let off passengers.
Floodlights were trained on one of the worst-damaged cars as rescuers tried to free four people still alive in the wreckage more than 11 hours after the 9:18 a.m. crash, said Yoshiki Nishiyama of the Amagasaki fire department. The four drank water provided to them, but their conditions were otherwise unknown.
The fate of the driver also was not known.
The seven-car commuter train was carrying 580 passengers when it derailed, wrecking an automobile in its path before slamming into a nine-story apartment complex just meters (yards) away. Two of the five derailed cars were flattened against the wall of the building, and hundreds of rescue workers and police swarmed the wreckage and tended to the injured.
''There was a violent shaking, and the next moment I was thrown to the floor ... and I landed on top of a pile of other people,'' passenger Tatsuya Akashi told public TV network NHK. ''I didn't know what happened, and there were many people bleeding.''
Train operator West Japan Railway Co. apologized.
The Amagasaki Fire Department said the death toll had reached at least 52, while a Hyogo prefectural (state) police official said at least 417 people had been taken to hospitals. It was not clear how many of the dead were passengers or if bystanders and apartment residents were among the victims.
The accident was the worst rail disaster in nearly 42 years in safety-conscious Japan, which is home to one of the world's most complex, efficient and heavily traveled rail networks. A three-train crash in November 1963 killed 161 people in Tsurumi, outside Tokyo.
''There are many theories but we don't know for sure what caused the accident,'' Chief Cabinet Secretary Hiroyuki Hosoda said. ''The prime minister instructed us to respond with urgency.''
Survivors said the force of the derailment sent passengers tumbling. Photos taken by an NHK reporter aboard the train showed passengers piled on the floor and some clawing to escape. Two derailed train cars smashed into the first-floor parking garage of the apartment complex, NHK said.
Distraught relatives rushed to hospitals to search lists of the injured and dead. Takamichi Hayashi said his elder brother, 19-year-old Hiroki, had called their mother on a mobile phone from inside one of the train cars just after the crash but remained unaccounted for. He said he had heard Hiroki was among the four trapped in the wreckage.
It was unclear how fast the train was traveling at the time of the accident, said Tsunemi Murakami, the train operator's safety director.
He estimated that it would need to have been traveling at 82 mph to have jumped the track purely because of excessive speed. The crash occurred at a curve after a straightaway, requiring the driver to slow to a speed of 43 mph.
A crew member aboard told police later he ''felt the train was going faster than usual,'' NHK said, echoing comments from survivors interviewed by the network who speculated that the driver was attempting to make up for lost time after overrunning a stop line at the previous station.
The driver had committed a previous overrun at a station in June 2004 and was issued a warning, officials said.
Murakami later said investigators had found scrapes and other evidence of rocks on the tracks. But he said it was too early to say whether that was a factor in the crash.
Experts suspected speed was to blame.
''If the train hadn't hit anything before derailing ... the train was probably speeding. For the train to flip, it had to be traveling at a high speed,'' Kazuhiko Nagase, a Kanazawa Institute of Technology professor and train expert, told NHK.
NHK reported that the automatic braking system at that stretch of track is among the oldest in Japan. The system stops trains at signs of trouble without requiring drivers to take emergency action, but the older system can't halt trains traveling at high speeds, NHK said.
Tokyo dispatched Self-Defense Force soldiers to the disaster scene to assist. Prime Minister Junichiro Koizumi offered condolences to families of passengers who were killed, as did Emperor Akihito, in unusual unscripted remarks. Koizumi pledged that officials would do everything they could to prevent a recurrence of the crash.
''It's tragic,'' Transport Minister Kazuo Kitagawa said at the scene. ''We have to investigate why this horrible accident happened.''
Deadly train accidents are rare in Japan. Five people were killed and 33 were injured in March 2000, when a Tokyo subway hit a derailed train. An accident killed 42 people in April 1991 in Shigaraki, western Japan.
An earthquake in 2004 caused a bullet train to derail, the first since the high speed trains went into service 40 years ago.