One died and seven people were missing Sunday after an accident overnight in which two Japanese military helicopters apparently collided before crashing into the sea, officials said.

A spokesman for Japan's Self-Defense Force (SDF) confirmed the late Saturday incident to AFP and said that one person was rescued but later confirmed dead.

Defence Minister Minoru Kihara said rescuers "spotted what are believed to be part of the aircraft in the sea, and we believe that the two helicopters crashed."

"At this point the cause is unknown, but firstly we do our best to save lives," Kihara told reporters.

Hours later, Kihara told reporters that the crew member who was rescued "was confirmed dead."

He also said the ministry "discovered the flight recorders in places close to each other," and so "possibility is high that (the two helicopters) collided."

The helicopters appear to have crashed during night-time training of countering submarines off the Izu Islands in the Pacific Ocean, officials said.

"The flight recorders are being analysed" while officials are interviewing crew of a third helicopter that was joining the drill but was not involved in the accident, chief of staff Ryo Sakai of the Maritime Self-Defense Force (MSDF) told reporters.

Communication with one chopper was lost at 10:38 pm (1338 GMT) off the island of Torishima, and one minute later an emergency signal was received from this aircraft, broadcaster NHK reported.

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Around 25 minutes later, at around 11:04 pm, the military realised that communication with the other aircraft was also lost in the same area.

The Mitsubishi SH-60K helicopters from the MSDF are mainly based on and operate from naval destroyers.

The MSDF said as there were no other aircraft nor vessels in nearby waters, involvement of another country in the incident is unlikely, NHK added.

Japan is boosting defence spending and deepening cooperation with the United States and other countries in Asia in response to growing Chinese assertiveness in the region and an unpredictable North Korea.

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

In January 2022, a Japanese fighter jet crashed in waters off central Ishikawa region, killing two pilots on board.

And in 2019, an F-35A stealth jet crashed into the sea after taking off from northeastern Japan on a training mission, killing a pilot.

Last November an Osprey military aircraft belonging to the US military crashed off Japan, killing all eight people on board, in the latest of a string of fatal accidents.

This prompted a decision by the United States the following month to ground the tilt-rotor aircraft worldwide. Japan also grounded its fleet of the same aircraft.