An American F-15 fighter crashed into the sea after its pilot ejected from his plane off Japan's southernmost Okinawa prefecture on Tuesday, the US Air Force said.

"A Kadena-based F-15 aircraft developed a problem that ultimately resulted in the pilot ejecting from the aircraft over the Pacific Ocean approximately 70 miles (110 kilometres) east of Okinawa," the air force said, referring to the hub of American air power in the Pacific.

"US and Japanese rescue crews are responding to recover the pilot, who reportedly ejected safely and is in contact with rescue crews," the statement said, adding the cause of the incident would be investigated.

Japan's coast guard said it was involved in the rescue.

"We sent airplanes and patrol ships to the scene after we received a call for help from Kadena Air Base," an official told AFP.

"We heard the pilot, the only person who was aboard, parachuted down and is safe, hanging on to something" in the sea, he said.

Okinawa is the reluctant host to more than half of the 47,000 American service personnel in Japan, and the crimes, noise and risk of accidents associated with their bases regularly provoke irritation locally.