One Japanese naval crewman has died and seven others are missing after two helicopters crashed during a night-time drill in the Pacific Ocean.
The twin-engine Mitsubishi SH-60Ks were on anti-submarine training near the Izu Islands, 600km (372 miles) south of Tokyo, officials said.
Two flight recorders were discovered close to each other as was debris including parts of rotor blades.
Defence Minister Minoru Kihara said the cause of the accident was unknown.
"Firstly we do our best to save lives," Mr Kihara said adding the helicopters were "doing drills to counter submarines at night".
A crew member was taken from the waters but was confirmed to have died.
Communication with one helicopter was lost at 22:38 local time (14:38 BST) off the island of Torishima, broadcaster NHK reports.
One minute later an emergency signal was received from this aircraft.
After 25 minutes, the military realised communication with the other aircraft, also a Mitsubishi SH-60K, was lost in the same area.
The Mitsubishi SH-60K helicopters - based on the Sikorsky Seahawk - mainly operate from naval destroyers.
The navy said as there were no other aircraft nor vessels in nearby waters, involvement of another country in the incident was unlikely.
Japan is boosting defence spending and deepening cooperation with the US and other countries in Asia in response to growing Chinese assertiveness in the Taiwanese region.
In April 2023 a Japanese army helicopter with 10 people on board crashed off Miyako island in southern Okinawa.
The UH60 helicopter, known as a Black Hawk, had been surveying the local area at the time it disappeared.