A CAL FIRE helicopter passes over the setting sun as the Oak Fire burns near Darrah in Mariposa County, California. Reuters

The Oak Fire in central California broke out on Friday and is raging while parts of the United States remain in the grip of a sweltering heat wave.

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The fire in Mariposa County has engulfed 17,241 acres (6,977 hectares) and is 16 percent contained, Cal Fire, the state fire department, said.

"Fire crews are working aggressively using bulldozers, hand crews and aircraft," with only "minimal growth on the fire" seen on Monday, the department said.

Firefighters battle with the Oak Fire in the Jerseydale community of Mariposa County, California, on Monday. AP

It is the most destructive blaze so far this fire season, according to Cal Fire, destroying more than three times the acreage of the nearby Washburn Fire, which has been nearly 90 per cent contained.

But it pales in comparison to last year's Dixie Fire, which burned nearly one million acres.

"What we're seeing on this (Oak Fire) is very indicative of what we've seen in fires throughout California, in the West over the last two years," Jon Heggie, a Cal Fire battalion chief, told CNN.

"These fires are burning with just such a velocity and intensity, it makes it extremely challenging and extremely dangerous for both the public and the firefighters," Heggie said.

"It's moving so quickly it's not giving people a lot of time, and they sometimes are just going to have to evacuate with just the shirts on their back," he said.

Firefighters mop up hot spots while battling fire in the Jerseydale community, California, on Monday. AP

Jonathan Pierce, a spokesman for the fire department, said low humidity and high temperatures were stoking the blaze.

The high number of dead trees and steep slopes in the area was also "leading to extreme fire behaviour," he added.

The Oak Fire has forced the evacuation of some 3,000 people so far, officials said.

More than 2,000 firefighters backed by 17 helicopters have been deployed against the fire near the southwestern edge of Yosemite National Park.

Agence France-Presse