Naval Air Crewman 2nd Class Joseph Rivera, a search and rescue swimmer looking out of a US Navy MH-60 Seahawk, helped conduct the search and rescue relief operations.
CNN  — 

At least one US Marine is dead and eight others are missing after a training accident involving an amphibious vehicle off the coast of Southern California.

The effort to find them has concluded after an extensive 40-hour search following the incident Thursday, the 1st Marine Expeditionary Force said. Officials determined there was little probability of a successful outcome.

“It is with a heavy heart, that I decided to conclude the search and rescue effort,” said Col. Christopher Bronzi, a commanding officer.

Sixteen people were aboard the vehicle Thursday when they reported taking water in the vicinity of the San Clemente Island, officials said.

In addition to the eight missing service members, at least one Marine was reported dead and two others injured that day, the Marines said at the time.

Five others made it back aboard their ship, said Gen. David Berger, commandant of the US Marine Corps.

“I’ve directed an immediate suspension of amphibious assault vehicle water operations until the causal factors of this mishap are better understood,” Berger said.

The incident occurred during a 15th Marine Expeditionary Unit and Makin Island Amphibious Ready Group routine training exercise.

The amphibious assault vehicle weighs approximately 26 tons, and is believed to have sunk to the ocean floor, which is hundreds of feet deep in that location. The AAV is below the depths where divers can go, so the Navy is assisting and providing resources that can go down and take a look at the vessel, according to Marine Lt. Col. Jody Osterman.

The Marines who were found were wearing normal combat gear including body armor, Osterman said. That includes an inflatable vest. Some of the Marines who were picked up were floating in the ocean.