A United States Navy aircraft carrying 11 crew and passengers crashed into the ocean southeast of Okinawa at about 2:45 p.m. Japan time, the Navy said.
The aircraft was en-route to the U.S. Navy aircraft carrier USS Ronald Reagan, which is currently operating in the Philippine Sea.
The Navy's Japan-based 7th Fleet said in a statement that a search and rescue operation was launched from the carrier.
"Personnel recovery is underway and their condition will be evaluated by USS Ronald Reagan medical staff," the statement said.
The names of the crew and passengers are being withheld pending next of kin notification.
The cause of the crash is not known at this time, the Navy said.