Firefighters struggled to contain an exploding Northern California wildfire under blazing temperatures as another heatwave blanketed the western United States, prompting an excessive heat warning for inland and desert areas.

Death Valley in southeastern California’s Mojave Desert reached 53 degrees Celsius (127F) on Saturday, according to the National Weather Service’s reading at Furnace Creek. The shockingly high temperature was actually lower than the previous high of 54C (129F).

If confirmed as accurate, the 54C reading would be the highest recorded there since July 1913, when Furnace Creek desert hit 57C (135F), considered the highest measured temperature on Earth.

About 483km (300 miles) northwest of the sizzling desert, the largest wildfire of the year in California was raging along the border with Nevada. The Beckwourth Complex Fire – a combination of two lightning-caused fires burning 72km (45 miles) north of Lake Tahoe – showed no sign of slowing its rush northeast from the Sierra Nevada forest region after doubling in size between Friday and Saturday.

Pushed by strong winds, a wildfire in southern Oregon doubled in size to 311 square km (120sq miles) on Saturday as it raced through heavy timber in the Fremont-Winema National Forest near the Klamath County town of Sprague River.

The California Independent System Operator warned of potential power shortage, not only because of mounting heat, but because a wildfire in southern Oregon was threatening transmission lines that carry imported power to California.

In Southern California, a brush fire sparked by a burning big rig in eastern San Diego County forced evacuations of two Native American reservations on Saturday.

In north-central Arizona, Yavapai County on Saturday lifted an evacuation warning for Black Canyon City, an unincorporated town 66km (43 miles) north of Phoenix, after a fire in nearby mountains no longer posed a threat.

In Mohave County, Arizona, on the same day two firefighters died after an aircraft they were in to respond to a small wildfire crashed, local media reported.

A wildfire in southeast Washington grew to almost 155sq km (60sq miles) as it blackened grass and timber while it moved into the Umatilla National Forest.

In Idaho, Governor Brad Little declared a wildfire emergency on Friday and mobilised the state’s National Guard to help fight fires sparked after lightning storms swept across the drought-stricken region.