A US Osprey military aircraft carrying six people on board has crashed into the waters off southwestern Japan. One person is confirmed dead. A rescue effort by the Japanese coast guard is underway.

The crash occurred just before 3 p.m. local time on Wednesday near the island of Yakushima.

Japan's defense ministry says US officials are calling the incident an attempted emergency water landing.

According to an eyewitness, the aircraft appeared to roll over mid-flight before descending vertically towards the water.

The eyewitness said, "It was like the so-called inverted flight. After it turned over, a fire broke out from the propeller on the left wing. There was an explosion right after that. Then the aircraft went straight down without gliding.

Japan's coast guard spotted what appeared to be wreckage from the aircraft. Local fishing boats helping with the rescue operation found three people in the nearby waters.

Defense Ministry officials say the aircraft is a CV-22 Osprey which belongs to the US Yokota Air Base in Tokyo. They say it was likely heading to the US Kadena Air Base in Okinawa.

The US deployed the Ospreys to Japan in 2018. CV-22s are mainly used to transport special forces. They have been involved in a number of serious accidents.

In 2010, an Osprey crash-landed in Afghanistan, killing 4 soldiers.

In 2012, a crash during a training mission injured five crew members in Florida.

In August last year, the aircraft were grounded by the US over a safety issue - but the flights were eventually resumed.