At least two other people were injured in the incident, which occurred Thursday, according to a tweet from the 1st Marine Expeditionary Force.
Search and rescue efforts are ongoing on Friday morning with the support of the Navy and Coast Guard.
All service members in the incident are assigned to the 15th Marine Expeditionary Unit, based off Camp Pendleton.
“We are very saddened by this tragic incident,” Col. Christopher Bronzi, the commanding officer of the 15th MEU. “I ask that you keep our Sea, the Sailors, and their families in your prayers as we continue our search.”
This is a breaking story and will be updated.