Firefighters make progress battling massive California blaze near Yosemite

Firefighters made progress battling California's largest wildfire of the summer on Tuesday, with more than one-quarter of the blaze near Yosemite National Park contained.

The Oak Fire in central California broke out on Friday and spread rapidly, destroying 41 buildings and forcing thousands to evacuate.

By Tuesday, nearly 3,000 firefighters and 24 helicopters at the scene had achieved some success containing the blaze, aided by slightly higher humidity levels, which are forecasted to increase further in the coming days.

Jonathan Pierce, a California fire department spokesman, told AFP that efforts to curtail the spread of the blaze could soon be aided as it approaches areas already ravaged by wildfires from recent years.

"If this fire hits the Ferguson fire scar, it will slow down a little bit because there is less fuel there," he said.

"That fire was as recent as 2018, so all the vegetation that has come back will be more thin than a lot of the vegetation that has not been burnt."

So far, the Oak Fire has burnt 18,000 acres -- the largest by area this year, but relatively minor compared to the mega-blazes that have engulfed hundreds of thousands of acres in recent years.

Its spread has been driven by an abundance of combustible fuel following years of drought and hot, dry weather conditions.

California Governor Gavin Newsom on Saturday declared a "state of emergency" in Mariposa County, citing "conditions of extreme peril to the safety of persons and property."

The Oak Fire is burning just a few miles from the smaller Washburn Fire, which briefly threatened Yosemite's rare giant sequoia trees earlier this month.

In recent years, California and other parts of the western United States have been ravaged by huge and fast-moving wildfires, driven by a warming climate.

The fire comes as the usually cooler Pacific Northwest is in the grip of extreme temperatures, forecast to top 100 degrees F (38C) in parts of Oregon.

Parts of the South-Central United States including Texas are also experiencing sweltering heatwaves.

But the Southwest is seeing monsoonal moisture, bringing heavy showers and thunderstorms to parts of the region, including sections of Arizona and Utah.