A U.S. Marine perished and eight other military servicemen - specifically seven Marines and a Navy sailor - are missing following a mishap involving an amphibious assault vehicle off Southern California's coastal waters, Thursday.

The AAV was reported to be taking on water at 5:45 p.m. local time Thursday and sank completely, the assumption being that the massive steel vehicle went all the way to the bottom, Lt. Gen. Osterman, the One Marine Expeditionary Force commanding general, disclosed in a media briefing Friday afternoon.

The search continued late Friday following a deadly accident during a training exercise off San Clemente Island, officials said. But the AAV vehicle is under hundreds of feet of ocean water, making rescue efforts very difficult for the eight missing troops.

Two Marines who were among those rescued sustained injuries, with one in critical condition in a hospital, and the other in stable condition, a Marine Corps statement said. Military ships and helicopters searched in high winds and choppy waters. The Navy-owned island is roughly 70 miles offshore from San Diego.

Marine Corps commandant, Gen. David Berger, said the search and rescue efforts were ongoing while he ordered the suspension of seaborne operations of all of its over 800 AAVs across the branch until the cause of the accident is determined. Berger said the move was out of "an abundance of caution."

The troops had just completed a routine training drill and were on their way back to the Navy ship with around 12 other AAVs when the accident happened, Gen. Osterman said. Troops aboard two other amphibious attack vehicles immediately responded but were unable to stop the 26-ton vehicle from sinking, the general said.

Col. Christopher Bronzi, commanding officer of the 15th Marine Expeditionary Unit, said they 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," Bill Bostock and Ryan Pickrell of Business Insider quoted Bronzi as saying in their report.

This is not the first time Marines deployed at Camp Pendleton have been wounded or killed during training with AAVs, which are heavy armored troop vehicles that transport small units from ship to shore. In 2011, a Marine was killed when an AAV in a training drill sank off the shores of Camp Pendleton. In 2017, 15 Marines were hurt when their AAV caught fire in a military drill.

The Marine Expeditionary Force is the Marine Corps' primary war-fighting group. There are three such organizations, which are composed of air, ground, and logistics forces.