Military authorities are investigating a Wednesday morning training accident at Camp Pendleton that sent 15 Marines to multiple area hospitals after their amphibious assault vehicle caught on fire.
Six have now been listed in critical condition at two different civilian hospitals. Six more were listed in serious condition.
Eight of the 15 Marines injured were sent to the burn center at the University of California San Diego medical center.
Four of the injured were taken to University of California Irvine medical center in Orange County.
One Marine has been taken to Scripps Memorial Hospital La Jolla and is in stable condition.
Two Marines went to Camp Pendleton Naval Hospital with minor injuries.
"Our thoughts and prayers are with the Marines and their families as they receive medical care," a Marine Corps statement said on Wednesday afternoon.
Officials with the 1st Marine Division said that the service members were hurt in the San Mateo section of the sprawling base during the scheduled land-based portion of a pre-deployment Marine Corps Combat Readiness Evaluation involving an Assault Amphibious Vehicle, or "Amtrack."
The Marines involved were from 1st Battalion, 1st Marine Regiment and 3rd Assault Amphibian Battalion.
Officials confirmed that the armored Amtrack caught on fire.
In 2013, a Marine at the Mojave Desert base in Twentynine Palms died and four others were injured when their Amtrack caught fire.
That accident was caused by ordnance ignition. The fatal incident led to the Marine Corps installing a safer and more efficient mine-clearing system on the vehicles earlier this year, according to dodbuzz.com.
The massive, tracked vehicles are designed to plunge through the water and then roll up onto shore, carrying Marines from ship to land.
They can carry more than 20 Marines inside, with a three-person crew.
The Corps has used these Amtracks since the 1970s. A new version, called the Amphibious Combat Vehicle, is under development.
In the meantime, the Marines are upgrading the older vehicles with buoyant armor, blast-mitigating seats and spall liners to make them last longer.
The upgrade also includes fuel tank protection and automotive and suspension improvements to maintain land and sea mobility regardless of the added weight.
Division spokesman 1st Lt. Paul Gainey said that the Corps will continue to provide updates as more details about the mishap become available.
Military investigators continue to probe a recent pair of fatal training incidents at Camp Pendleton.
On Aug. 5, Lance Cpl. Cody J. Haley, 20, was crushed by a falling tree while he performed routine morning physical training. The Iowa native was assigned to 1st Battalion, 4th Marines.
Pfc. Michael Philomeno Giannattasio, 22, of Armada, Mich., was found unresponsive on Aug. 30 during land navigation training on the Basic Reconnaissance Course.