A helicopter that crashed in Nagano Prefecture on Sunday, killing all nine members of the rescue crew on board, may have come into contact with trees on a mountain ridge before going down, officials said Tuesday.

Nagano Prefectural Police, who are investigating the accident on suspicion of negligence resulting in death, found damage to the aircraft that suggests an impact with trees.

Some 120 police personnel were dispatched to the site where the helicopter went down as part of the probe to ascertain the cause of the crash.

Also on Tuesday, investigators from the Japan Transport Safety Board, an arm of the transport ministry, arrived at the site to investigate the incident.

Autopsies are being carried out on the victims of the accident.

Video footage of the flight taken by a crew member on board showed that the helicopter went down before the start of a rescue exercise.

The recording shows that a problem occurred within 15 minutes of takeoff before communications were lost, the Nagano Disaster Prevention Air Corps said.

The police said the helicopter was found around 1,700 meters up the 1,929-meter-high Mount Hachibuse, which straddles the cities of Matsumoto and Okaya. Investigators found damage on trees on a mountain ridge just above the crash site that appeared to have been caused by the rotary wing from a helicopter. Parts of the aircraft were scattered near the trees, the police said.

Prefectural police, will further analyze the video footage and examine the flight plan and maintenance records.

According to the prefectural government, the helicopter took off from Nagano's Shinshu Matsumoto Airport at around 1:30 p.m. on Sunday. The crash was discovered at around 3:10 p.m. the same day.

The team was set to conduct a drill that simulated the rescue of mountain climbers, with members descending from the helicopter using ropes.