A Nagano Prefectural Government rescue helicopter with nine people aboard crashed in a mountainous area near Shiojiri in the prefecture Sunday, local authorities said.

Three of those aboard were found and later pronounced dead. Two others were trapped in the helicopter and were unconscious. Police and rescuers are still trying to confirm the whereabouts of the other four.

The helicopter was conducting a mountain rescue drill at the time of the crash, according to the prefecture.

The helicopter was carrying seven firefighters, a pilot and an engineer, all prefectural personnel, according to the prefecture. They were all men. The pilot, in his 50s, was a veteran who has been flying the same helicopter since 1997.

Nothing was found to be wrong with the helicopter when it underwent a checkup just before it departed from Matsumoto airport on Sunday.

According to its flight plan, the helicopter was scheduled to depart from Matsumoto at 1:33 p.m. and arrive at a helipad in Takabocchi highland 20 minutes later.

According to a weather agency official, the local weather wasn't rough at that time.

A person at Shinshu University Hospital, where one of the crew in his 50s was pronounced dead, said that the man died instantly after hitting his head and other parts of his body hard when the helicopter crashed.

Trees at the crash site were damaged and parts of the helicopter were scattered over the snow-covered slope. The pilot's seat was crushed and the helicopter's tail broke off.

A police search team found the helicopter at around 3:10 p.m.

The transport ministry will dispatch three investigators to the site to find out the cause of the accident.