The five crew members were rescued after the aircraft landed "in shallow water" off the coastline of Camp Schwab around 10 p.m. local time, according to a statement from III Marine Expeditionary Force.
The Marines, from Marine Aircraft Group 36, 1st Marine Aircraft Wing, were airlifted in an HH-60G Pave Hawk helicopter flown by members of the 33rd Rescue Squadron at Kadena Air Base to a naval hospital at Camp Foster, where they received medical treatment.
The Corps is investigating the mishap.
Officials with III MEF initially posted a pair of tweets about the crash. The first confirmed that an Osprey mishap had occurred; the second reported that all crew members of the downed aircraft had been transported to the naval hospital.
This is the second time in a week that a Marine Corps aircraft has crashed near Japan.