TOKYO: A U.S. military aircraft carrying eight people crashed into the sea in Japan on Wednesday, killing at least one crew member.

The U.S. military said the mishap occurred during a routine training mission off the shores of Yakushima Island, about 1,040 km (650 miles) southwest of the capital Tokyo.

"The crew’s conditions are unknown at this time," a statement from U.S. Air Force Special Operations Command said.

Japan's coast guard said what appeared to be wreckage from the tilt-rotor V-22 Osprey and one person, who was later confirmed to have died, were found about 3 km (2 miles) from the shore.

A representative for the Yakushima Fisheries Cooperative initially said fishing boats in the area found three people in the surrounding waters, but later clarified that just one person had been found.

Another Osprey thought to have been travelling with the crashed aircraft landed safely at the island's airport on Wednesday afternoon, a spokesperson for the local government said.

The United States has more than 50,000 U.S. troops in Japan, many in the strategically important southwestern Okinawan islands, amid growing Chinese military assertiveness around nearby Taiwan.

The crash happened just before 3 p.m. (0600 GMT), with witnesses saying the aircraft's left engine appeared to be on fire as it approached an airport for an emergency landing, despite clear weather and light wind, media reported.

The aircraft was part of a unit based in Okinawa trained to transport and supply special operations forces, according to the U.S. military.

Japan, which also operates Osprey aircraft, said on Wednesday it had asked the U.S. military to investigate the crash.

Developed jointly by Boeing BA.N and Bell Helicopter, the Osprey can fly both like a helicopter and fixed-wing aircraft and is operated by the U.S. Air Force, Marines and Navy and the Japan Self-Defense Forces.

The deployment of the hybrid aircraft in Japan has been controversial, with critics saying it is prone to accidents. The U.S. military and Japan say it is safe.

In August, a U.S. Osprey crashed off the coast of northern Australia while transporting troops during a routine military exercise, killing three U.S. Marines.

Another crash-landed in the ocean off Japan's southern island of Okinawa in December 2016, prompting a temporary U.S. military grounding of the aircraft.