Emergency declared as wildfire rages near Yosemite National Park

San Francisco:  Authorities have declared a state of emergency in part of California as a wildfire continued to rage near the Yosemite National Park.

The state of emergency has been declared in Mariposa County and in a statement, California Governor Gavin Newsom said the flames were being "driven by hot, dry weather and drought conditions".

The fast-moving wildfire, dubbed the Oak Fire, grew to 6,555 acres (about 26.5 square km) overnight, prompting mandatory evacuation orders, Xinhua news agency.

The wildfire ignited on Friday afternoon in Mariposa County and was still zero contained as of Saturday, according to the California Department of Forestry and Fire Protection (Cal Fire).

It is about 50 km away from Yosemite Valley, near Yosemite National Park, one of the most popular national parks in the US.

The blaze had destroyed at least 10 structures and damaged another five by Saturday, threatening 2,000 other structures, Cal Fire said.

"Fire activity is extreme with frequent runs, spot fires and group torching. Emergency personnel are working to safely evacuate people and are actively engaged in protecting structures," said Cal Fire, noting that explosive fire behaviour is challenging over 400 firefighters on the spot.

It is now "one of California's largest wildfires of the year", the Los Angeles Times said in a report.

Some residents were forced to temporarily evacuate and some roads in the area, including one major highway to Yosemite, were closed.

With the Oak Fire, the streak of relatively modest and non-destructive wildfires in California so far this season appears to be over, said Daniel Swain, a climate scientist at the University of California, Los Angeles.

He added that record vegetation dryness and less stable atmospheric conditions will likely favour plume-dominated behaviour at times.

Swain estimated that the Oak Fire will very likely surpass 10,000 acres (around 40.46 square km) in less than 24 hours.

Another explosive wildfire, the Washburn Fire, has burned over 4,850 acres (19.6 square km) to date with 79 per cent contained in over two weeks near Yosemite National Park.

The Washburn Fire has drawn national attention as hundreds of firefighters are battling the blaze to protect some of the world's oldest and largest trees in the park.

Must of the US is sweltering through a heat wave this weekend.

Temperatures in Mariposa County hit 35.5 degrees Celsius on Saturday, and are expected to stay at that level for the next few days.