Some 13,000 residents are leaving their homes as nearly two dozen wildfires rage across drought-parched California.
More than 9,000 firefighters are trying to dampen the 21 conflagrations.
The biggest inferno, the Rocky Fire, jumped over a highway that had served as a containment line on Monday afternoon.
It has reduced to smouldering ashes more than 62,000 acres (25,000 hectares) north of Sacramento, the state capital.
The blaze tripled in size over the weekend to almost 97 square miles (250 square km), feeding on its own winds.
The Rocky Fire, which is only 12% contained, razed 20,000 acres in just five hours, stunning the authorities.
"The term that I'm using is 'historic'," one firefighter told CNN.
"The reason I say that is that there are firefighters who have 25, 30 years on the job who have never seen fire behaviour like we've seen the last couple of days."
Two dozen homes have been destroyed over the past few days.
The California blazes killed a firefighter last week and injured four others.
A total of some 142,000 acres have burned so far.
The wildfires prompted California Governor Jerry Brown to declare a state of emergency last week.
Lightning strikes in the drought-stricken state were blamed for the fires.