Californian officials warned on Saturday that "historic and extreme" wind conditions were set to fan raging wildfires in the north of the state, as millions of residents face power cuts.
Governor Gavin Newsom declared a state of emergency as the so-called Kincade Fire spread to 9 591 hectares after breaking out on Wednesday in the Sonoma wine region.
The blaze, which is burning in remote steep terrain, has destroyed about 50 structures and forced the evacuation of the small community of Geyserville and of nearby vineyard operations.
"This is definitely an event that we're calling historic and extreme," David King, meteorologist for the US National Weather Service, told Saturday's Los Angeles Times.
"What's making this event really substantial... is the amount of time that these winds are going to remain."
Hot, intense winds are expected to pick up on Saturday and last into Monday.
The state's largest utility, Pacific Gas & Electric Co, said it expected to cut off power to 850 000 customers - a precautionary shutdown that local media say would affect about two million people.
"The weather event could be the most powerful in California in decades," PG&E said, with dry northeast winds forecast to gust up to 112km.
"PG&E will need to turn off power for safety several hours before the potentially damaging winds arrive," it added.
"Winds of this magnitude pose a higher risk of damage and sparks on the electric system and rapid wildfire spread."
About 1 300 firefighters battled the Kincade Fire, which is only five percent contained, according to the California Department of Forestry and Protection.
'Don't know what to do'
"I can't explain it," 70-year-old Tina Tavares, who was evacuated from her Geyserville home, told the San Francisco Chronicle.
"It's like you're in a bad earthquake, the ground is opening up... and you're seeing it and don't know what to do."
PG&E has come under fierce scrutiny after it reported that even though power had already been shut down to nearly 28 000 customers in Sonoma County this week, some high-voltage transmission lines were still operating when the fire broke out.
The same type of lines was responsible for California's deadliest wildfire ever - last year's Camp Fire, which killed 86 people.
PG&E, which filed for bankruptcy protection earlier this year, has been blamed for several other fires in the state in recent years.
Governor Newsom hit out at the company on Friday, saying it had put "profits over the people of California for too long".
He said it was "infuriating beyond words" that a state such as California had to endure blackouts.
"It's about dog-eat-dog capitalism meeting climate change," he said, referring to PG&E. "It's a story about greed, and they need to be held accountable."
Further south in California, tens of thousands of residents near Santa Clarita, just north of Los Angeles, evacuated their homes this week as the so-called Tick Fire scorched over about 1 600 hectares.
The blaze forced the shutdown of all schools in the area as well as a major freeway, creating traffic chaos for commuters.
Some 1 325 firefighters backed by air tankers and helicopters battled the flames close to densely packed communities, with 10 000 structures at threat, officials said.
Six homes were destroyed, though the number was expected to rise.
Wildfires also erupted over the border in Mexico's Baja California state, where local civil protection authorities said on Friday that three people had been killed and over 150 homes destroyed.
The state's director of civil protection, Antonio Rosquillas, said that the municipality of Tecate, bordering the United States, was worst hit.