A home is seen fully engulfed in flames during the Glass Fire in St. Helena, California, US. File/Reuters

Thick smoke that held down winds and temperatures began to clear on Sunday, with three people reported missing and thousands fleeing the advancing flames.

California has grown to become the second-largest wildfire in state history as firefighters battling braced for a return of fire-friendly weather.

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The winds weren’t expected to reach the ferocious speeds that helped the Dixie Fire explode in size last week. As of Sunday, the fire had destroyed 489,287 acres (198,007 hectares), authorities said, up from the previous day's 447,723 acres.

This photo combination shows the Dixie fire in the Indian Falls neighbourhood of unincorporated Plumas County. AFP

Over the weekend, it surpassed the 2018 Mendocino Complex Fire to make it the second-worst fire in state history.

"The live trees that are out there now have a lower fuel moisture than you would find when you go to a hardware store or a lumber yard and get that piece of lumber that’s kiln dried,” Mark Brunton, operations section chief for the California Department of Forestry and Fire Protection, said in an online briefing on Sunday morning.

The Dixie Fire, which has incinerated more than 463,000 acres. AFP

"It’s that dry, so it doesn’t take much for any sort of embers, sparks or small flaming front to get that going.”

The Dixie blaze, which on Saturday left three firefighters injured, remained 21 percent contained Sunday, unchanged from the day before, the CalFire website reported.

Crews estimate the fire, which began July 13, will not be fully extinguished for two weeks.

Photo shows the burned vehicle during the Dixie Fire near Greenville, California, on Sunday. AFP

With smoke clearing out on eastern portions of the fire, crews that had been directly attacking the front lines would be forced to retreat and build containment lines farther back, said Dan McKeague, a fire information officer from the US Forest Service. On the plus side, better visibility should allow planes and helicopters to return to the firefight and make it safer for ground crews to maneuver.

"As soon as that air clears, we can fly again,” McKeague said.