The death toll in Japan's worst rail accident in four decades looked set to rise to more than 100 on Wednesday as hopes faded that more survivors would be found in the wreckage 48 hours after a packed commuter train jumped the tracks and crashed into an apartment complex.

The official death toll stood at 91 after rescue crews extracted 18 bodies from a mangled carriage overnight.

But there was little hope for the dozen or so people still trapped inside another carriage, embedded in a ground-floor car park under the building on the outskirts of the city of Osaka.

"Unfortunately, time has passed but we're carrying on and have not given up," said a fire department official.

Rescue teams were using equipment to detect heart beats with electromagnetic waves.

Police raided the offices of the train's operator on Tuesday looking for clues to the cause of the crash, which investigators said could have been linked to excessive speed after the train's driver fell more than a minute behind schedule.

The government, keen to avoid any erosion of confidence in a rail system that transports more than 21 billion people a year, pledged to ensure the safety of the country's railways.

"The government as one, will do its utmost to find out the cause of the accident and prevent a reoccurrence," Transport Minister Kazuo Kitagawa told parliament.

Even as he spoke, news emerged that a commuter train in Yokohama, near Tokyo, had collided with a van at a crossing.

None of the train's passengers was hurt, but the van's driver was taken to hospital in serious condition.

On Tuesday, another passenger train hit a truck at another crossing near Tokyo. The truck driver suffered minor injuries.

Investigations into Monday's crash were focusing on speed as well as other factors such as rail design that might have caused the packed train to jump the tracks as it rounded a curve.

Data recorded in the train's system showed it was traveling at 62 miles an hour as it approached the site of the accident, where the speed limit was 43 mph. But analysts said speed alone would not likely have led to the disaster.

CUTTING CORNERS?

Police investigating for possible professional negligence hauled away boxes of documents from the offices of West Japan Railway Co. (JR West).

JR West, which was completely privatized a year ago, has been trying to improve profitability by cutting costs, leading to speculation it may have cut corners on safety.

"Efficiency is necessary, but safety cannot be sacrificed in return for efficiency," Kitagawa said.

The automatic train stop system in the area was of the oldest type and had no ability to apply automatic brakes if a passing train was going too fast, the Transport Ministry said.

Analysts said the accident could have been caused by a number of factors, alone or in combination, such as a malfunctioning brakes, faulty rails or driver error.

JR West has said there were marks on the tracks of the type left when a train runs over an object such as a stone, but added that it was not clear if this was related to the accident.

The train had overshot the previous station by about 130 feet and had to reverse back to the platform.

The driver, a 23-year-old man with 11 months' experience, is presumed to have died in the crash.

The same driver also over-shot a station by 328 feet last June, railway officials said.

The accident was the worst for Japan's heavily used rail network since 1963 when about 160 people were killed in a multiple train collision, and the most serious since Japan's rail network was privatized in 1987.

JR West shares were unchanged on Wednesday after falling a total of about five percent on Monday and Tuesday.

PHOTO CAPTION

A worker walks past as a machine removes the wreckage of a derailed train at the site of the train that smashed into an apartment building in Amagasaki, western Japan April 26, 2005. (Reuters)