Oak Fire in California threatens Yosemite as US faces heatwave

North-western state of Alaska also fending off rare number of wildfires

Firefighters mop up hot spots while battling the Oak Fire in California on July 25. AP

A firefighter battles the Oak Fire in the Jerseydale community of Mariposa County, California. AP

Firefighters cool down a controlled area near Yosemite National Park. AP

A Nasa image shows smoke from wildfires raging near Yosemite National Park in California on July 24. EPA

A firefighter battles the Oak Fire on July 24. AP

A helicopter drops water on the Oak Fire as it burns in Mariposa County, California. AP

The Oak Fire burns in northern California. AP

A firefighter tries to control a backfire operation to slow the Oak Fire advancing on a hillside. Bloomberg

More than 3,000 people have had to flee their homes because of the Oak Fire. Reuters

An Alaskan airplane drops water on the Clear Fire near Anderson, Alaska, on July 6. AP

Alaska's wildfire season includes more than 530 blazes that have burnt an area more than three times the size of Rhode Island. AP

California firefighters on Monday were fighting to slow the spread of a major wildfire that was threatening to engulf parts of America's famous Yosemite National Park.

The Oak Fire in northern California, which comes as a record heatwave has settled over large parts of the US, expanded from 650 hectares to 4,845 hectares on Friday, local news site SFGate reported, and has grown to at least 8,000 hectares since then.

Its continued spread has made it the state's largest wildfire this year and has forced more than 3,000 people to flee.

Another wildfire in Yosemite earlier this month threatened the park's sequoia trees.

Drought and warming temperatures mean California now experiences catastrophic wildfires all year. The western state has seen both its largest and deadliest wildfires in history in the past five years.

Cal Fire, the state's firefighting agency, on Monday said it did not know the cause of the Oak Fire, but that it has contained about 10 per cent of the blaze.

Governor Gavin Newsom declared a state of emergency and issued financial assistance to Cal Fire.

Further north, Alaska has reported more than 540 wildfires in a record season that has only just begun.

The largest US state often battles brush fires each year, but the large number this early in the season is unheard of, with numbers on track to surpass the historic wildfire seasons of 2015, 2004 and 2005.

Firefighters across the country are also facing a record-breaking heatwave.

The heatwave hit the north-east region of the country particularly hard at the weekend, with temperatures nudging 40º Celsius. Other regions are expected to experience extreme heat throughout the week.