Hundreds of firefighters are being deployed in northern California as hot winds renew the threat of fire in a region where massive blazes have already destroyed hundreds of homes and killed dozens of people.
Most of the huge fires that erupted over the past eight weeks are now largely contained and skies once stained orange by heavy smoke are blue again.
Containment means firefighters have lines holding in a fire, though it doesn't mean it has stopped burning.
But the gains made by thousands of firefighters assigned to the blazes that have scorched 1.6 million hectares this year could be hampered if new fires ignite, says Cal Fire assistant deputy director Daniel Berlant.
"If a new fire breaks out, it will be able to grow very quickly under these conditions," he said on Wednesday.
The National Weather Service issued a red-flag for extreme danger through Friday morning, with bone-dry humidity and wind gusts up to 90 km/h.
Pacific Gas & Electric, the largest utility in the nation, warned it may cut power starting on Wednesday evening to as many as 54,000 customers in 24 counties.
The strategy aim to prevent fires being started by power lines that have been damaged or knocked down in high winds.
"We really view it as a last resort option," said Mark Quinlan, the company's incident commander.
The utility has also deployed generators and other measures to keep electricity flowing in some areas that might lose power during the outages.
About 33,000 homes and businesses could begin losing power at 6 pm, mainly in the Sierra Nevada foothills and northern San Francisco Bay Area, followed by 21,000 more two hours later, along with customers in portions of California's central coast.
All power should be restored by late Friday night, PG&E said.
The outages would include regions already hit by massive wildfires this and in recent years.
The Glass Fire that ravaged the Northern California wine country of Napa and Sonoma counties was surrounded on Wednesday after destroying more than 1,500 homes and other buildings.
Farther north, the Zogg Fire in Shasta and Tehama counties was fully contained.
More than 8500 wildfires have burned more than 16,000 square km in California since the start of the year, most since mid-August. Thirty-one people have died, and more than 9,200 buildings have been destroyed.