The search continued on Monday for seven missing Japan Maritime Self-Defense Force members after two helicopters crashed during a late-night anti-submarine drill in the Pacific on Saturday, with Prime Minister Fumio Kishida vowing an "all-out" rescue effort.

The Defense Ministry is analyzing two flight recorders that were recovered from an area where the search is taking place, but there has so far been no data indicating an abnormality in either of the helicopters, Defense Minister Minoru Kihara told reporters.

The two SH-60K patrol helicopters, which the ministry believes likely collided, were carrying four people each, with one confirmed to have died on Sunday.

Flight recorders from two Maritime Self-Defense Force SH-60K patrol helicopters recovered from waters east of Torishima Island in the Izu Island chain are pictured on April 21, 2024. (Photo courtesy of the Maritime Self-Defense Force)(Kyodo)

A source involved in the fact-finding said the two helicopters did not use a system that would have enabled them to share information with each other, such as their respective positions, before the accident.

"It is a matter of greatest regret that we lost a valued (MSDF) member during difficult nighttime exercises to prepare for missions," Kishida told a parliamentary committee on Monday.

"Taking this serious incident into our heart, we will take all possible measures to ensure the safe operations of Self-Defense Forces aircraft," he said.

The crash came as the country bolsters its security amid China's increasing maritime assertiveness. It was the latest in a string of fatal accidents involving Japan's Self-Defense Forces aircraft in recent years.

Kihara said he issued an order on Sunday to the SDF to carefully conduct preflight checks on all aircraft, carry out safety management education and confirm emergency procedures.

In the latest incident, the helicopters lost contact at 10:38 p.m. and 11:04 p.m. on Saturday, respectively, with the MSDF receiving an emergency signal at 10:39 p.m.

Together with another MSDF helicopter, the two crashed aircraft were conducting a drill to detect and attack a submarine after taking off from separate destroyers deployed nearby.

A total of three helicopters were in the air at the time, with Adm. Ryo Sakai, chief of staff of the MSDF, saying the third aircraft that did not crash "may have been in a position to have objectively witnessed the circumstances" of the incident.

The crash site is in waters around 270 kilometers east of Torishima Island in the Izu island chain, where the water depth is about 5,500 meters.

Rotor blades and other helicopter parts have been spotted on the surface, as well as helmets.

Sakai said the exact locations of the helicopters' main wreckage are still unknown but acknowledged that "common sense" would suggest they had sunk deep down in the sea.

The accident is a blow to the Japanese Self-Defense Forces, which in April 2023 saw a UH-60JA helicopter of the ground force crash into waters off an island in the southern prefecture of Okinawa, resulting in the deaths of all 10 people aboard.

In January 2022, an Air Self-Defense Force F-15 fighter jet crashed into the Sea of Japan off Ishikawa Prefecture in the central part of the country, killing two pilots.

Defense Minister Minoru Kihara (L) holds a press conference at the ministry in Tokyo on April 22, 2024, as Maritime Self-Defense Force Chief of Staff Adm. Ryo Sakai looks on. (Kyodo) 

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