US authorities said Saturday they were searching for five people missing as a huge wildfire raged in northern California, leaving two towns in little more than cinders.

The Dixie Fire, the largest active wildfire in the United States, recently became the third-largest in California history.

As of late Saturday it had destroyed 447,723 acres (180,782 hectares) in four counties, up from the previous day's 434,813 and surpassing the vast Bootleg Fire in southern Oregon.

Dixie is now 21 percent contained, the CalFire website reported, adding that three firefighters had so far been injured fighting the blaze.

While the fire continued to grow, officials said Saturday that cooler, calmer weather was giving firefighters a much-needed break.

Those conditions are expected to continue into Sunday.

"We expect the same fire behavior as yesterday, which was fairly moderate," Jake Cagle, a firefighter sections chief, said in a briefing Saturday.

Earlier, the Dixie Fire left the Gold Rush town of Greenville charred and in ruins, while also burning through the small town of Canyondam.

The Plumas County sheriff's office said it had received descriptions of five people considered missing in Greenville and was searching for them.

Five other missing people were confirmed found on Saturday.

- Residents refuse to leave -
As authorities urge thousands of locals to evacuate, they have been met at times by armed residents refusing to budge, the Los Angeles Times reported Saturday.

Law enforcement officers are asking any residents who stay for the names of next-of-kin -- to be notified if the fire claims their lives.

The Dixie Fire's movement northeastward has been slowed in part because it has reached the "scar" of an earlier blaze, the 2007 Moonlight Fire, reducing available fuel, CalFire said.

More than 5,000 personnel are now battling the Dixie blaze, which is sending enormous clouds of smoke into the air that are easily visible from space.

A preliminary investigation has suggested the fire was started when a tree fell on a power cable owned by regional utility Pacific Gas & Company (PG&E), a private operator that was earlier blamed for the huge Camp Fire in 2018, which killed 86 people.

By late July, the number of acres burned in California was up more than 250 percent from 2020 -- itself the worst year of wildfires in the state's modern history.

A long-term drought that scientists say is driven by climate change has left much of the western United States parched -- and vulnerable to explosive and highly destructive fires.