Five US Marines are missing after two Marine Corps aircraft collided in mid-air and crashed into the sea off the coast of Japan in what US officials say may have been a refuelling exercise gone wrong.
Japan's defence ministry said its maritime forces had so far found two of the seven Marines who were aboard the aircraft - an F/A-18 Hornet fighter jet and KC-130 Hercules - at the time of Thursday's incident.
One was in a stable condition at Marine Corps Air Station Iwakuni, while the second had been found about 10 hours after the collision and brought aboard a Japanese military vessel, the ministry said.
No other details about the second Marine were known, a ministry spokesman said.
Search and rescue efforts for the remaining five continued.
The incident adds to a growing list of US military aviation accidents around the world in recent years, prompting hearings in Congress to address the rise.
The Military Times reported earlier this year that aviation accidents jumped nearly 40 per cent from fiscal years 2013 to 2017. At least 133 service members were killed in those incidents, it said.
"The incident is regrettable, but our focus at the moment is on search and rescue," Japanese Defence Minister Takeshi Iwaya told a news conference. "Japan will respond appropriately once the details of the incident are uncovered."
The Marine Corps said in a statement the incident occurred around 2am local time in Japan about 322km off the Japanese coast.
The two aircraft had launched from Marine Corps Air Station Iwakuni and were conducting regular training when there was a "mishap," the Marine Corps said.
The Marine Corps did not elaborate on the nature of the incident. A US official, speaking on condition of anonymity, said it occurred during a refuelling exercise.
An investigation has begun.