The U.S. military aircraft and boats scoured waters off Australia's east coast for three Marines involved in what the Marines Corps called a "mishap" with an MV-22 aircraft.
"The aircraft involved in the mishap had launched from the USS Bonhomme Richard (LHD 6) and was conducting regularly scheduled operations when the aircraft entered the water," the Marine Corps said in a statement.
23 of the 26 personnel on board have been rescued, the statement added.
According to the Marine Corps, small boats and aircraft from the 31st Marine Expeditionary Unit and Bonhomme Richard Expeditionary Strike Group carried out the search and rescue operation.
The Marine authorities are investigating the incident.
United States President Donald Trump and Australian Prime Minister Malcolm Turnbull have been briefed up on the situation.
The Australian authorities said no Australian personnel were on board.
The U.S. military has been in the area for training exercises with the Australian military. The recent joint military exercise took place largely in Shoalwater Bay and involved more than 30,000 U.S. and Australian personnel, according to Australian Defence Department.
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