OSAKA - At least 50 people died and 417 others were injured when five of seven rapid commuter train cars derailed Monday morning in Amagasaki, Hyogo Prefecture, sending two cars slamming into an apartment building, police and firefighters said.

The accident occurred at around 9:20 a.m. near a railway crossing between Amagasaki and Tsukaguchi stations on West Japan Railway Co.'s Fukuchiyama Line.

The first and second cars of the train crashed into the ground floor of the nine-story apartment building, located about 6 meters from the curved tracks, and were badly damaged.

More than 10 people remain trapped in the wreckage, the firefighters said. Rescuers have yet to locate the whereabouts of the train driver.

Four survivors have been found, and the firefighters were still trying to rescue them Monday night. Doshisha University and Doshisha Women's College in Kyoto Prefecture said jointly that at least 25 of their students were injured in the accident, some seriously.

Of the 50 people killed, 27 were men and 23 were women, the police said.

The train, carrying about 580 people, was heading from Takarazuka Station in Hyogo Prefecture to Doshishamae Station in Kyoto Prefecture.

Government and JR West officials said they are looking into the cause of the accident.

The number of deaths surpassed the 42 people killed in the 1991 head-on collision of two trains in Shiga Prefecture, making Monday's accident the worst since the JR companies were launched in 1987 after the privatization of the now-defunct Japan National Railways.

JR West said it found marks on the tracks often left when a train runs over an object such as a stone, but added it has confirmed no causal relationship with the accident.

It said it has found marks that indicate the train derailed some 60 meters away from the apartment building.

The speed limit at the accident site was 70 kilometers per hour but it is unknown how fast the train was traveling when the accident occurred, JR West officials said.

The automatic train stop system set up in the area was of the oldest type, which had no ability to apply automatic brakes in the event a passing train by was speeding, the Ministry of Land, Infrastructure and Transport said.

The train overran the stop before the accident site, Itami Station, by about 8 meters and had to back up before allowing passengers to get on and off, a JR West official said. It left Itami Station about 90 seconds behind schedule and passed Tsukaguchi Station about one minute late, he said.

The conductor was reporting to the command room about the Itami Station overrun when the accident occurred, JR West said. The conductor immediately told the command room via mobile phone, ''We've just had a derailment accident,'' according to JR West.

Numerous injured passengers said the train seemed to be traveling faster than usual after leaving Itami Station, as if hurrying to make up for the delay.

JR West sources suggested the train may have been traveling over the speed limit and failed to negotiate the curve.

Based on calculations, a train traveling at the site of the accident would derail if it were moving at 133 kph or more, JR West officials said. The train in question was structurally designed to move at a maximum speed of 120 kph, they said.

The Hyogo prefectural police set up a special investigative team to look into the accident.

Atsushi Shibagaki, 33, a company employee in the second car that smashed into the apartment building, said, ''The end of the train body popped up after a large bang. I fell on my back and scraped all over my face.''

Michi Yamashita, 14, who suffered a fractured left hand, said, ''We were all smashed to the left side of the train at the moment the accident occurred. Passengers broke open a crack in the train body so we could go outside.''

The 23-year-old train driver, 11 months on the job, overshot a station stop by 100 meters last June, JR West said.

The 42-year-old conductor on the train was interviewed by the police, JR West officials said.

JR West President Takeshi Kakiuchi apologized for the accident, saying at a news conference in Osaka, ''As a railway operator, I am filled with a very sorry feeling.''

In Tokyo, Prime Minister Junichiro Koizumi said at his office he has told the related organizations to coordinate closely with each other in dealing with the incident.

In response to requests by the Hyogo prefectural government, the Ground Self-Defense Force unit in the prefecture dispatched troops to help rescue victims, and nearby municipalities such as Osaka and Kobe sent firefighters to provide emergency aid.

The central and local governments have set up headquarters and offices to gather information and deal with the accident.

Land, Infrastructure and Transport Minister Kazuo Kitagawa inspected the accident site Monday afternoon, and the ministry's Aircraft and Railway Accidents Investigation Commission dispatched five inspectors.

Initial information was conflicting about whether the train cars derailed before or after colliding with an automobile near the crossing, which was equipped with a breaker and alarm signals.

The police said the train likely derailed before hitting a car parked in a parking lot as there was no sign of impact on the tracks, but the transport ministry initially said the train derailed as a result of hitting the car.

JR West said it is not known whether the derailment or collision happened first.