Thousands of firefighters battle California wildfire burning near Yosemite National Park

A destructive wildfire near Yosemite National Park in central California burned out of control through tinder-dry forest on Sunday and had grown into one of the state'sbiggest blazes of the year, forcing thousands of residents to flee remote mountain communities.

Some 2,000 firefighters battled the Oak Fire, along with aircraft and bulldozers, facing tough conditions that includes steep terrain, sweltering temperatures and low humidity, according to the California Department of Forestry and Fire Protection, or Cal Fire.

"It's hot out there again today," Cal Fire spokesperson Natasha Fouts said Sunday. "And the fuel moisture levels are critically low."

Crews on the ground protected homes as air tankers dropped retardant on 15-metreflames racing along ridgetops east of the tiny community of Jerseydale.

Light winds blew embers ahead into tree branches "and because it's so dry, it's easy for the spot fires to get established and that's what fuels the growth," Fouts said.

The fire erupted Friday southwest of the park near the town of Midpines in Mariposa County. Officials described "explosive fire behavior" on Saturday as flames made runs through bone-dry vegetation caused by the worst drought in decades.

By Sunday the blaze had consumed more than 56 square kilometresof forest land, with no containment, Cal Fire said. The cause was under investigation.

Evacuations were in place for over 6,000 people living across a several-kilometre span of the sparsely populated area in the Sierra Nevada foothills, though a handful of residents defied the orders and stayed behind, said Adrienne Freeman with the U.S. Forest Service.

"We urge people to evacuate when told," she said. "This fire is moving very fast."

Lynda Reynolds-Brown and her husband Aubrey awaited news about the fate of their home from an evacuation centre at an elementary school. They fled as ash rained down and the fire descended a hill towards their property.

WATCH | Massive wildfire in central California forces thousands from their homes:

Wildfires prompt evacuations in California as millions in U.S. under heat warnings

2 years ago

Duration 2:00

Nearly 85 million Americans are under heat warnings issued by the U.S. weather service. The extreme heat is continuing to fuel wildfires, with one blaze raging through central California.

"It just seemed like it was above our house and coming our way really quickly," Reynolds-Brown told KCRA-TV.

Gov. Gavin Newsom proclaimed a state of emergency for Mariposa County due to the fire's effects.

Flames destroyed at least 10 residential and commercial structures and damaged five others, Cal Fire said. Assessment teams were moving through mountain towns to check for additional damage, Fouts said.

Numerous roads were closed, including a stretch of State Route 140 that's one of the main routes into Yosemite.

California has experienced increasingly larger and deadlier wildfires in recent years as climate change has made the West much warmer and drier over the past 30 years. Scientists have said weather will continue to be more extreme and wildfires more frequent, destructive and unpredictable.

Pacific Gas & Electric said on its website that more than 3,100 homes and businesses in the area had lost power as of Sunday and there was no indication when it would be restored. "PG&E is unable to access the affected equipment," the utility said as flames roared Friday.

The Oak Fire was sparked as firefighters made progress against an earlier blaze, the Washburn Fire, that burned to the edge of a grove of giant sequoias in the southernmost part of Yosemite National Park. The 19-square-kilometrefire was nearly 80 per centcontained after burning for two weeks and moving into the the Sierra National Forest.