The Marines were aboard a small amphibious craft that took on water.

One Marine was killed and eight service members are missing when the amphibious assault vehicle (AAV) they were on sank in the waters off the California coast during a training exercise late Thursday afternoon, according to the Marine Corps.

The incident occurred around 5:45 p.m. PT in the vicinity of West Cove on San Clemente Island, a defense official said. Located 80 miles off the coast of Southern California, the island is managed by the U.S. Navy and frequently used by the Navy and Marine Corps for training.

Two others were injured in the incident.

Fifteen Marines and a sailor were aboard the AAV as it made its way back to the U.S. Navy amphibious ship USS Somerset, according to three defense officials.

The AAV was spotted taking on water and “submerging rapidly,” one official said.

Rescue efforts were immediately launched and eight of the 16 personnel aboard were recovered from water.

A Marine rescued later died at Scripps Memorial Hospital La Jolla, according to officials. Two injured Marines were taken to local hospitals. One is in critical condition and the other is in stable condition.

Multiple ships and helicopters from the U.S. Navy and U.S. Coast Guard have been combing the waters off of San Clemente Island looking for the missing service members.

The Marines were from the 15 Marine Expeditionary Unit (MEU), I Marine Expeditionary Force, that is based at Camp Pendleton, north of San Diego.

The Marines use amphibious assault vehicles to carry out beach landings. The small armored craft are launched from U.S. Navy amphibious ships and convert into armored personnel carriers after arriving on land.

“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,” said Col. Christopher Bronzi, the commander of the 15th MEU.

Mishaps with AAVs are not a common occurrence. There have been 10 to 15 reported incidents over the past 20 years and the last reported fatality involving an AAV in water occurred in January of 2011.

“San Clemente is a very challenging amphibious training ground,” said Eric Oehlerich, an ABC News contributor and former Navy SEAL who has conducted training on the island. “Night amphibious training is some of the most complex and high risk training you can do as an amphibious soldier.”

According to Oehlerich, the high surf conditions around the island can be tricky to navigate in an AAV, particularly at night.

Marine Expeditionary Units (MEUs) are typically composed of 2,200 Marines that travel aboard three Navy amphibious ships that form an Amphibious Ready Group.

The Marines will stay aboard the ships during six-month deployments to specific regions of the world. During that time they can use the aircraft or landing craft aboard the ships to get to land locations for short-notice deployments or scheduled training.

The mishap occurred as the 15th MEU was training with the USS Makin Island Amphibious Ready Group that includes the USS Somerset and USS San Diego.