Thousands of firefighters are battling a blaze in California that is generating its own weather system, with authorities warning on Monday that the conditions could worsen.

Around 5,400 firefighters have been struggling to contain the inferno but could contain just 22% of it by late Monday, the California fire and forestries department reported.

The flames have grown large enough to create clouds that can cause lightning and high winds, which in turn fan the fire, according to experts.

"If these clouds get tall enough they do have the potential to produce lightning," warned Julia Ruthford, a government meteorologist assigned to the blaze.

The Dixie Fire has been raging in the forests of northern California since mid-July, part of a climate crisis that has brought sweltering heat and an alarming drought. Over the weekend it merged with another fire, prompting new evacuation orders.

Dixie is "the largest fire I've seen in my life," a local was quoted as saying but he added that he does not plan to evacuate and is prepared to fight the blaze himself if it reaches his property.

"A lot of people think we're foolish," the local said of his family's decision to stay.

But "you don't leave the safety of your family in the hands of strangers."

Wildfires are common in the state but this summer has been particularly incendiary.

Fires have already ravaged three times more vegetation this year than they had at this time in 2020, the worst fire year in California's history.

Rescue workers have been dispatched from as far away as Florida to help contain the Dixie Fire and its pyrocumulus clouds.

Despite its size -- the fire's circumference stretches at least 82 miles and it has burned 197,487 acres -- it has so far ravaged remote areas, destroying the few dozen homes and small buildings in its path.

Moving along steep slopes, the firefighters sometimes ride a train from which they can spray water on otherwise inaccessible areas.

But in these weather conditions, "the embers can really easily travel a mile ahead of the fire," Rick Carhart, a spokesman for the firefighters, was quoted by AFP as saying.