California fires spread in July 4 weekend heat wave

California firefighters battled multiple blazes in record heat Friday, with a new fire breaking out near the famous Yosemite National Park even as a larger inferno further north came under control.

Temperatures up to 117 degrees Fahrenheit (47 degrees Celsius) were recorded in the western US state Friday, as the region's latest heat wave nears its peak.

"Dangerous heat is likely to become more widespread in the West today and Saturday... Temperatures will be 15-30 degrees above average for much of the West Coast today," warned the National Weather Service.

"Widespread temperature records are expected to be tied or broken," the NWS said.

The excessive heat comes on the July 4 weekend, when millions of Americans celebrate the anniversary of their nation's independence with displays of fireworks that can spark blazes in hot, dry conditions.

A fast-moving fire erupted just outside Yosemite National Park late Thursday, causing large parts of the former Gold Rush town of Mariposa to be evacuated.

By Friday afternoon, the fire had burnt nearly 1,000 acres (405 hectares) and was 15 percent contained, according to Cal Fire.

"Winds have calmed which has helped firefighters make progress overnight," it said.

Some residents had been allowed to return to their homes. The fire's cause was not yet known.

There was also progress in northern California, where earlier this week thousands of people were ordered to evacuate from the Thompson Fire near Oroville.

Despite some of the region's highest temperatures, firefighters reported success in containing the blaze, with some evacuation orders lifted.

Still, fire officials and forecasters warned that the danger is far from over, with high temperatures expected to spread further and to peak Saturday.

"The duration of this heat is also concerning as scorching above average temperatures are forecast to linger into next week," warned the NWS.

Climate scientists say the western US is undergoing a decades-long aridification as weather patterns change, at least in part because of human-caused global warming.