Bone-dry conditions could lead to rapid spread of California's largest wildfire

California's largest wildfire continued to grow Wednesday while thousands of firefighters prepared for a tougher fight as dangerous weather returns.

A red flag warning was issued through Thursday because of hot, bone-dry conditions, with winds up to 64 km/h. That could drive flames through timber, brush and grass, especially along the northern and northeastern sides of the vast Dixie Fire.

"I think we definitely have a few hard days ahead of us," said Shannon Prather,with the U.S. Forest Service.

Firefighters were able to save homes and hold large stretches of the blaze. But flames jumped perimeter lines in a few spots Tuesday, prompting additional evacuation orders for about 15,000 people east of Lake Almanor, fire officials said.

Firefighters were protecting the small northern California mountain community of Greenville as the three-week-old fire grew to more than 1,108 square kilometresacross Plumas and Butte counties.

Heat from the flames created a pyrocumulus clouda massive column of smoke that rose more than nine kilometres in the air, said Mike Wink, a state fire operations section chief.

Dawn Garofalo watched the cloud grow from the west side of the lake, where she fled with a dog and two horses, from a friend's property near Greenville.

"There's only one way in and one way out. I didn't want to be stuck up there if the fire came through," Garofalo said.

From her campsite on the lake bed, she watched the fire glowing on the horizon before dawn. "The flames were huge. They must have been 500 feet high. Scary," she said.

The fire has threatened thousands of homes and destroyed 67 houses and other buildings since breaking out on July 14. It was 35 per cent contained.

WATCH | More evacuations in California due to wildfires:

Fast-growing wildfire in northern California prompts more evacuations

3 years ago

Duration 0:50

Firefighters are trying to hold back raging flames in Plumas County, Calif. as thousands more residents must abandon their homes to escape.(Noah Berger/AP Photo)

About 240 kilometresto the west, the lightning-sparked McFarland Fire threatened remote homes along the Trinity River in the Shasta-Trinity National Forest. The fire was only fiveper cent contained. It had burned fiercely through nearly 65 square kilometresof drought-stricken vegetation.

Weather warnings

Similar risky weather was expected across southern California, where heat advisories and warnings were issued for interior valleys, mountains and deserts for much of the week.

Heat waves and historic drought tied to climate change have made wildfires harder to fight in the American West. Scientists say climate change has made the region much warmer and drier in the past 30 years and will continue to make weather more extreme and wildfires more frequent and destructive.

More than 20,000 firefighters and support personnel were battling 97 large, active wildfires covering 7,560 square kilometresin 13 U.S. states, the National Interagency Fire Center said.

Montana on Tuesday had 25 active large blazes, followed by Idaho with 21 and Oregon with 13. California had 11.