Seven of the crew members on the Japanese navy choppers remain unaccounted for since the April 20 crash, with one confirmed dead.

"Analysis of flight recorders show that...the two helicopters recorded the same things at the same time at the same place -- same latitude and longitude -- which means it was a collision," Defence Minister Minoru Kihara told reporters.

"We didn't find data that show any abnormality of the aircrafts," he said, adding that training flights using the same type of helicopter would resume on Friday.

The navy's "accident investigation committee will continue probing" the cause and how the accident occurred, he said.

The SH-60K helicopters each with four crew on board were conducting submarine location drills late on April 20 in deep waters off the Izu Islands in the Pacific Ocean.

Soon after the incident rescuers found one person who was later confirmed dead, along with debris and flight recorders, but there has been no trace of the seven missing crew.

The Self-Defence Forces suspended training using the SH-60K helicopters after the accident.

In April last year a Japanese army UH-60JA helicopter with 10 people on board crashed off Miyako island in southern Okinawa. There were no survivors.