MARINE CORPS BASE CAMP PENDLETON, Calif. -- OCEANSIDE - Eight Miramar-based Marines were injured, two of them seriously enough to be life-flighted, when three vehicles from their convoy collided in the southbound lanes of Interstate 5 Sunday near a rest stop south of the Las Pulgas Road exit.

Mercy Air flew Lance Cpls. Blake Lubic, 20, of La Mesa, and Jesus Ortiz, 22, of San Diego, to Scripps Memorial Hospital in La Jolla, where they were treated and released.

Six other Marines were also treated and released. Five were treated at Naval Hospital Camp Pendleton, the other at Tri City Hospital in Oceanside, after being transported by ambulance.

The Marines, all from 4th Medical Battalion, a Marine Corps Reserve unit headquartered at Marine Corps Air Station Miramar, were returning from weekend training when the accident occurred.

The lead humvee swerved to avoid a civilian van that was towing another vehicle and had pulled only halfway off the side of the roadway, accident victims said.

The second humvee stopped safely, as did the 7-ton truck following behind it. The trailing vehicle, another 7-ton, was not able to stop in time. It smashed into the third vehicle, which was shoved into the second vehicle, said Capt. Robert Barber, the reserve unit's assistant inspector-instructor.

"I tried to stop, but couldn't. (There was) too much weight," said Lance Cpl. Anthony Sanchez, who was driving the last vehicle, a 7-ton truck that was towing an almost-full water tank trailer.

"It gave me an extra push," said 20-year-old Sanchez, a truck driver from Pomona.

Before police and paramedics arrived, Navy Hospital corpsmen traveling with the rest of the unit's convoy began treating the injured at the scene, Sanchez said.

"The corpsmen were there and on the ball. They were taking care of everybody," Sanchez said.

Emergency service personnel from the base, as well as the California Highway Patrol, closed down two highway lanes after arriving on the scene.

After checking over the injured Marines, medics called for Mercy Air to transport the two most seriously hurt Marines. When the helicopter arrived, police closed down all of the southbound lanes to provide a clear place to land, said Officer Phil Konstantin, from the CHP traffic management center.

Consequently, traffic on I-5 was backed up for about five miles, said traffic reporter Laura Dorman from the Metro Network traffic-reporting agency.

"When you shut down a freeway, it's hideous," Dorman said.

All the injured Marines were treated and released later that day, said Barber, 30, from Opelika, Ala.