The firefighters had just wrapped up a 12-hour shift fighting a wildfire.
Eight firefighters were injured when the fire truck they were driving in rolled over as it returned from battling the Airport Fire wildfire, one of several large blazes raging in Southern California.
The vehicle crashed while traveling north at about 6:50 p.m. on State Route 241 near Portola Parkway in Irvine, California, Orange County Fire Authority Chief Brian Fennessy said. Other vehicles weren't involved with the crash, he added.
The injured were taken to four different hospitals, Fennessy said. Seven were transported by ambulances and one was airlifted by helicopter from the scene, he added. Two of the injured were in stable condition at Hoag Hospital Irvine and six were taken to trauma centers, he said.
The firefighters, which he described as a "hand crew," had just wrapped up a 12-hour shift fighting the wildfire, he said.
"We'll be here for our firefighters, and we ask that you pray for our firefighters and their families," Fennessy said during a press conference. "All the families have been notified, and this is the beginning of a long road for many of those firefighters and our fire department."
The California Highway Patrol told ABC News' Los Angeles station KABC that a vehicle driving in front of the truck swerved to avoid hitting a ladder that was in one of the lanes, causing the fire vehicle to swerve, lose control and overturn after hitting the guard rail.