Three days after the fires began, firefighters were still unable to gain control of the blazes, fuelled by the return of strong winds, that had turned entire Northern California neighbourhoods to ash and destroyed at least 3,500 homes and businesses.
"We are literally looking at explosive vegetation," said Ken Pimlott, chief of the California Department of Forestry and Fire Protection. "It is very dynamic. These fires are changing by the minute in many areas."
Some 73 helicopters, 30 air tankers, 550 firetrucks and nearly 8,000 firefighters were being used, Mr Pimlott said.
In neighbouring Sonoma County, authorities issued an evacuation advisory for the northern part of the town of Sonoma and the community of Boyes Hot Springs.
"That's very bad," resident Nick Hinman said when a deputy sheriff warned him that the driving winds could shift the wildfires toward the town of Sonoma proper, with 11,000 residents. "It'll go up like a candle."
Ash snowed over the Sonoma Valley, covering windshields, as winds began picking up toward the potentially disastrous forecast speed of 30 mph.
The wildfires ranked as the third deadliest and most destructive in state history. And officials warned the worst was far from over.
The fires have burned through 265 square miles of urban and rural areas.
High winds and low humidity made conditions ideal for fire on the start virtually anywhere on ground that was parched from years of drought.
California Department of Forestry and Fire Protection spokesman Daniel Berlant said 22 wildfires were burning Wednesday, up from 17 the day before.
As the fires grow, officials voiced concern that separate fires would merge into even larger infernos.
"We have had big fires in the past. This is one of the biggest, most serious, and it's not over," Governor Jerry Brown said at a news conference, alongside the state's top emergency officials.
In Southern California, cooler weather and moist ocean air helped firefighters gain ground against a wildfire that has scorched more than a dozen square miles.