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

Ten ships and five aircraft from the Japan Maritime Self-Defense Force were combing the waters, aided by others from the Air Self-Defense Force and the coastguard, a navy duty official told AFP.

"We have a 24-hour operation for the search, which took place all day and all night," the navy officer said.

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

"It is a matter of the utmost regret that we lost our important personnel as they engaged in a very tough, late-night training which was conducted in order to fullfil their duties," Prime Minister Fumio Kishida told a televised legislative committee session on Monday.

Defence Minister Minoru Kihara said that there was so far no information from the flight recorders to suggest any technical problems with the aircraft.

Navy chief of staff Ryo Sakai cancelled a planned visit to China, where he was to attend the Western Pacific Naval Symposium.

Communication with one of the helicopters was lost at 10:38 pm Saturday off the island of Torishima, and one minute later an emergency signal was received from this aircraft, broadcaster NHK reported.

Around 11:04 pm, the military realised that communication with the other aircraft was also lost in the same area.

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