A search and rescue operation is under way in Japan after an incident involving two US Marine Corps aircraft.
The planes involved are a KC-130 and an F/A 18 based at Iwakuni near Hiroshima and are carrying seven personnel, Marines officials said.
The Marine Corps tweeted that the incident occurred at about 02:00 on Thursday (17:00 GMT Wednesday).
US media say the two planes crashed during midair refuelling but this has not been officially confirmed.
The Marine Corps said the planes had taken off from Marine Corps Air Station Iwakuni and “were conducting regularly scheduled training when the mishap occurred”.
Some media reports said the incident happened off the coast.
Japanese search and rescue aircraft have responded to the incident.
The KC-130 is an extended-range tanker version of the C-130 and is used for mid-air refuelling.
The McDonnell Douglas F/A-18 Hornet is a fighter and attack aircraft and can carry a wide range of missiles and bombs.
The US has more than 50,000 troops stationed in Japan, more than 18,000 of them in the US Marine Corps.