Amid a heat wave warning, new wildfires are sweeping the western United States, forcing hundreds of families from their homes, US authorities said Monday.

Near Los Angeles, the fire dubbed the “Line Fire” grew over the weekend after it broke out on Thursday. It burned more than 80,000 acres of barren countryside and is spreading into an area close to tourist spots.

Tens of thousands of homes are under threat and several roads have been closed in the face of the huge flames that are spreading across the bush-filled hills, despite the efforts of more than 1,700 firefighters.

Another fire, the “Bridge Fire”, broke out on Sunday afternoon. By Monday morning, it had burned 12,000 acres, causing the authorities to issue evacuation orders.

The dangerous heat that is plaguing the region is making it difficult for the firefighters to fight on the ground and in the air.

The mercury has topped 43 degrees in many parts of the American West in recent days. And gusts of wind accelerate the spread of fires.

The heat warning remains in effect until the end of the day.

“Dangerous heat is forecast for at least one more day in southern California and parts of the Southwest,” the National Weather Service (NWS) warned.

Fire danger will remain “high to critical across much of the region over the next two days,” he added, noting “the combination of above-average temperatures, dry vegetation and gusty winds.”

In northern California, another small but near-residential fire forced 4,000 people to evacuate their homes. The Boyles Fire, near Clearlake, has already burned 30 buildings and destroyed 50 vehicles, according to local firefighters.

In neighboring Nevada, the Davis Fire destroyed 65,000 acres of vegetation near Reno. At least 12,000 residents of the southern part of this city were forced to leave their homes and a dozen buildings were damaged.

Images posted on social media show dozens of wild horses escaping the flames.

The fire forced Democrat Tim Walsh, Kamala Harris’ White House deputy, to cancel a meeting he had planned for Monday night in Reno.