Washington (AFP) - Five crewmembers aboard a US Marine MV-22 Osprey in Japan were injured Tuesday when the tilt-rotor aircraft suffered a "mishap" and landed in shallow water, the Pentagon said.

The aircraft conducted a "landing in shallow water" off Okinawa near the US Marine base Camp Schwab, Pentagon spokesman Navy Captain Jeff Davis said.

He did not immediately have additional details about the incident or whether the Osprey had crashed.

"It constitutes a mishap," he said, noting that an investigation was underway.

The incident occurred around 10:00 pm local time (1330 GMT) and the crewmembers were airlifted to a US naval hospital.

The MV-22 Osprey is a tilt-rotor aircraft that can carry 24 Marine combat troops and combines the maneuverability of a helicopter with the speed and range of a turboprop plane.

The crewmembers in Tuesday's incident were assigned to Marine Aircraft Group 36, 1st Marine Aircraft Wing.