It took place during a routine training exercise in the area of San Clemente Island and Marines on the vessel reported taking on water at around 5:45 pm Thursday (0045 GMT Friday), a statement said.

Fifteen Marines and a sailor from the 15th Marine Expeditionary Unit were inside the vehicle, it said, adding that eight have been rescued.

One Marine was pronounced dead in hospital, while two others remained hospitalized -- one in critical condition and the other stable.

"Search and rescue efforts are ongoing to recover the remaining eight service members," the statement said, describing a major search operation involving the destroyer USS John Finn, three Navy and one Coast Guard helicopters and multiple small vessels.

"We are deeply saddened by this tragic incident. I ask that you keep our Marines, sailors, and their families in your prayers as we continue our search," Colonel Christopher Bronzi, the unit's commanding officer, was quoted as saying.