Japan's Coast Guard said one person had been found dead near the crash site. Japan's NHK broadcaster said the CV-22 Osprey hybrid plane had been trying to land at Yakushima Airport with one engine on fire. There is no US comment.

Ospreys - which can function as a helicopter and a turboprop aircraft - have been involved in a string of fatal crashes over the years.

The aircraft that went down on Wednesday was thought to be heading from Iwakuni base in the western Yamaguchi prefecture to Kadena base in the country's south-westernmost Okinawa region.

Japan's defence ministry said the aircraft disappeared from the radar at 14:40 local time (05:40 GMT) on Wednesday.

The Coast Guard received a distress call five minutes later, saying the plane had crashed.

It then sent six boats and two helicopters to the scene. At 16:00, the helicopters spotted what looked like a part of the plane and a life raft, a spokesperson told the BBC.

Earlier reports said eight people were on board the aircraft, but that number was later revised down by the Coast Guard.

It posted photos of what is believed to be the plane's wreckage off Yakushima.

An eyewitness told local TV that the plane had been circling before exploding and crashing into the sea on Wednesday.

Another Osprey aircraft believed to have been flying alongside landed safely at Yakushima, local officials said.