Two Japanese Maritime Self-Defense Force helicopters crashed during a drill in the Pacific Ocean late Saturday, leaving at least one of the eight crew members dead, with the other seven still missing, Kyodo News reported on Sunday.

The two aircraft, which crashed in waters around 270 kilometers east of Torishima Island in the Izu Island chain during a nighttime drill in the area, are believed to have collided with each other, Defense Minister Minoru Kihara told reporters.

The cause of the incident is still unknown but the defense ministry will do its utmost to search for and rescue those still missing, Kihara said.