Six firefighters remained hospitalized Friday after their truck rolled over on a highway on their way back from working a 12-hour shift battling one of three massive blazes burning in Southern California. Two others were released after the crash, officials said.

Orange County Fire Authority Chief Brian Fennessy said a total of eight firefighters were injured, and all are hand crew members who were returning from the Airport Fire Thursday evening when a ladder in the road caused the truck to swerve, strike a guardrail and overturn. The crash occurred on the California State Route 241 just north of Portola Hills.

“It is the most challenging assignment that anybody can be assigned to,” Fennessy told reporters Friday. “This is obviously a huge tragedy for our family.”

Two firefighters were stable and released Thursday night, he said.

“Many of the injured are going to be hospitalized for quite a while,” Fennessy said. He declined to discuss details of the injuries due to privacy laws.

Dr. Humberto Sauri, Orange County Global Hospital’s medical director of trauma services, where two firefighters are patients, said one is in critical and stable condition, and the other “quite critical,” He declined to provide further details.

The collision remains under investigation, California Highway Patrol Lt. Hope Maxson said.

With the blaze still burning, Ventura and Santa Barbara counties sent in hand crews to fill in, Fennessy said. The fire was 51 percent contained Friday morning, according to the California Department of Forestry and Fire Protection, or Cal Fire.

At least one firefighter was flown by helicopter, with others taken by ambulance to hospitals.

“All of our crews that were involved are going through a formal critical incident stress debriefing at our headquarters right now,” Fennessy said after the crash. “You can only imagine how traumatic it is for their brother and sister firefighter to see them injured like that on the freeway.”