It was unclear whether there were any survivors, but the coastguard said one unconscious person had been found at the scene and transported to a nearby port.

The unconscious person was found in the sea, the coastguard said, and resuscitation was being attempted.

Local media reported that the coastguard had spotted wreckage near the site of the crash.

"We received information at 2:47 pm (0547 GMT) today that the US military's Osprey crashed off Yakushima Island," a spokeswoman for the coastguard told AFP.

"We were also notified that there were eight crew members on board," she added.

An emergency management official in the Kagoshima region told AFP that "police received a report that an Osprey was spewing fire from a left engine and was landing at a beach near Yakushima Airport".

The coastguard said it has mobilised patrol ships and aircraft around Yakushima, which lies south of Japan's southernmost main island of Kyushu.

Japanese broadcaster NHK reported that the Osprey was on its way from the Iwakuni US base near Hiroshima in the Yamaguchi region headed for the Kadena base further south in Okinawa.

NHK also cited defence ministry sources as saying that the aircraft was a CV-22 Osprey belonging to the US Yokota air base in Tokyo.

Government spokesman Hirokazu Matsuno said Japan was "aware of information that the US military's Osprey fell out of radar (contact)" near Yakushima Island.

"The government is confirming the extent of damage and will prioritise saving human lives," Matsuno told reporters.

The US embassy in Japan was not immediately able to comment. The US military says it has about 54,000 personnel in Japan.

- Troubled history -

The Osprey, developed by Bell Helicopters and Boeing and which can operate like a helicopter or a fixed-wing plane, has suffered a string of fatal crashes over the years.

In August, a crash in northern Australia killed three US marines among the 23 on board.

The Boeing MV-22B Osprey crashed on Melville Island, north of Darwin during a military exercise for locally based troops. At the time the cause was unclear.

Four US Marines were killed in Norway last year when their MV-22B Osprey aircraft went down during NATO training exercises.

Three Marines were killed in 2017 when an Osprey crashed after clipping the back of a transport ship while trying to land at sea off Australia's north coast.

In 2016, an MV-22 Osprey crash-landed off Okinawa, prompting the US Marines to temporarily ground the aircraft in Japan after the accident sparked anger among locals.

And 19 Marines died in 2000 when their Osprey crashed during drills in Arizona.

- Other crashes -

There have been multiple other crashes of US military aircraft in recent years.

This month five US service members were killed when a helicopter crashed into the Mediterranean during a training exercise.

An F-35 stealth warplane went down in South Carolina in September, with the pilot able to eject.

In April, three US soldiers were killed and another injured when two helicopters returning from a training mission in a remote area of Alaska collided.

The previous month, two US Army helicopters crashed during a nighttime training mission in Kentucky, killing all nine soldiers on board.

tmo-hih-stu/mca

BOEING