A USA official told Fox News that seven Marines were on board the two aircraft. Search and rescue missions were being led by the Japanese Maritime Self Defense Forces, ABC News reported.
The U.S. Marine Corps said Thursday an FA-18 fighter and a KC-130 tanker aircraft were involved "a mishap" off the Japanese coast early Thursday. The pilot successfully ejected and was safely recovered by an Air Self-Defense Force search and rescue team.
It was unclear if U.S. military officials were also assisting with the search.
The planes involved are a KC-130 and an F/A-18 based at Iwakuni near Hiroshima and were carrying seven personnel, Marines officials said.
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Josef Patterson, a spokesman with the 3rd Marine Aircraft Wing, told Marine Corps Times. Naval Institute (USNI), at least one person has been rescued so far in what it called a collision between a KC-130J tanker and an F/A-18D fighter jet.
Rescuers found one of seven crew members, who were on-board the plans, in a stable condition and are still searching for the others, officials said.
The BBC's Rupert Wingfield-Hayes in Tokyo says that air-to-air refuelling is a hard and potentially unsafe flight operation, especially when done at night.
The US military has about 50,000 troops stationed in Japan and accidents are not uncommon.