US firefighters have condemned drone owners who flew their craft near forest fires and grounded helicopters being used to douse flames.
Lives were put at unnecessary risk because helicopters could not fly, said fire department officials.
The helicopters were helping to contain a large wildfire in San Bernadino county over the weekend.
Five drones spotted hovering over the fire were thought to be shooting video for their owners.
News footage of the fire shows people abandoning their cars to escape the flames as the fire engulfed Interstate 15 - a major road that links Los Angeles and Las Vegas. The fire destroyed 20 vehicles on the road and damaged 10 more.
More than 4,250 acres have been consumed by the fire which has been exacerbated by California's four-year drought.
The activity of the drones meant helicopters were grounded for about 20 minutes, Eric Sherwin of the San Bernadino fire department told CNN.
"Fifteen to 20 minutes were lost that could have led to another water drop cycle, and that would have created a much safer environment and we would not have seen as many citizens running for their lives," he said.
Hobby drones posed a "pose a major safety threat to firefighting pilots and firefighters", said an official incident report into the Interstate 15 fire.
"When a hobby drone is flown into a fire area, incident commanders have no choice but to suspend air operations and ground aircraft until the drone is removed from the area," it said.
A collision could damage aircraft, injure the pilot, crew or firefighters below, it warned. At worst, it said, drones could cause helicopters to collide in mid-air.
The fire department issued images that were shared on social media, warning drone owners to stay away from fires. "If you fly, we can't," they said.
US rules governing drone use mean any pilot caught flying their craft over a disaster area that has temporary flight restrictions in place could be fined up to $25,000 (£16,000). It is not clear whether the FAA is going to investigate who was piloting the drones over the Interstate 15 fire.
Drones have hindered firefighters in California at least four times before now, sometimes stopping flights for up to 90 minutes.