Firefighters are struggling to contain wildfires, fanned by hot desert winds, that forced the evacuation of tens of thousands of Orange County residents.
Two fires broke out in Southern California on Monday, critically wounding two firefighters and leading to 90,000 evacuations.
The larger blaze, the Silverado fire, had grown to more than 12,000 acres by noon on Tuesday local time.
A utility company said the fire may have been started by its equipment.
A spokesman for Southern California Edison said: “It appears that a lashing wire attached to a telecommunications line may have contacted SCE’s power line above it, possibly starting the fire.”
SCE is now investigating the incident, he added, and as a precautionary measure the company cut power to almost 19,000 homes and businesses.
The Silverado fire, in the foothills of Irvine, quickly spread after being fanned by strong winds and dry conditions.
More than 750 firefighters with 14 helicopters fought the fire, but only managed to contain 5% of it.
The two firefighters, aged 31 and 26, who were critically injured fighting the blaze suffered second and third-degree burns over much of their bodies, said the Orange County Fire Authority.
The other fire, dubbed the Blue Ridge fire, broke out near Yorba Linda and forced the evacuation of 8,700 households there, in Chino Hills and in Brea.
The Blue Ridge fire had burned through more than 15,200 acres by Tuesday morning.
The causes of California’s devastating wildfires have become a political battleground.
State Governor Gavin Newsom has blamed climate change while President Donald Trump has instead pointed to land management practices as the key driver.
An analysis by scientists, published last month, found an “unequivocal and pervasive” role for climate change in driving the scale and impact of wildfires in California.