Wildfires that torched homes and forced thousands of people to evacuate were burning across 10 parched Western states on Tuesday, with the largest, in Oregon, threatening California’s power supply.

Nearly 60 wildfires tore through bone-dry timber and brush from Alaska to Wyoming, according to the National Interagency Fire Centre, with Arizona, Idaho and Montana accounting for more than half of the large active blazes.

The fires erupted as the West was in the grip of the second bout of dangerously high temperatures in just a few weeks.

A climate change-fuelled megadrought is also contributing to conditions that make fires even more dangerous, scientists said.

The National Weather Service said the heatwave appeared to have peaked in many areas, and excessive-heat warnings were largely expected to expire by Tuesday. However, they continued into Tuesday night in some California deserts.

In Northern California, a combined pair of fires started by lightning, dubbed the Beckwourth Complex, was less than 25% surrounded after days of battling flames fuelled by winds, hot weather and low humidity that sapped the moisture from vegetation.

Evacuation orders were in place for more than 3,000 residents of remote northern areas and neighbouring Nevada.

There were reports of burned homes, but damage was still being assessed. The blaze had consumed 140 square miles (362 sq km) of land, including in Plumas National Forest.

A fire that began in the Sierra Nevada south of Yosemite National Park on Sunday exploded over 14 square miles (36 sq km) and was only 10% contained. A highway that leads to Yosemite’s southern entrance remained open.

The largest fire in the United States lay across the California border in south-western Oregon.

The Bootleg Fire – which doubled and doubled again over the weekend – threatened some 2,000 properties, state fire officials said. It had burned at least seven homes and more than 40 other buildings.

Over the weekend, the Klamath County Sheriff’s Office warned that it would cite or even arrest people who ignored orders to “go now” in certain areas immediately threatened by the blaze.

Tim McCarley told KPTV-TV that he and his family had been ordered to flee their home on Friday with flames just minutes behind them.

“They told us to get the hell out ’cause if not, you’re dead,” he said.

He described the blaze as “like a firenado”, with flames leaping dozens of feet into the air and jumping around, catching trees “and then just explosions, boom, boom, boom, boom”.

The fire was burning in the Fremont-Winema National Forest, near the Klamath County town of Sprague River. It had ravaged an area of about 240 square miles (621 sq km), or nearly twice the size of Portland.

Firefighters had not managed to surround any of it as they struggled to build containment lines.

The fire drastically disrupted service on three transmission lines providing up to 5,500 megawatts of electricity to California, and the state’s power grid operator repeatedly asked for voluntary power conservation during the evening.

Elsewhere, a forest fire started during lightning storms in south-east Washington grew to 86 square miles (223 sq km). It was 20% contained on Monday.

Another fire west of Winthrop closed the scenic North Cascades Highway, the most northern route through the Cascade Range. The road provides access to North Cascades National Park and the Ross Lake National Recreation Area.

In Idaho, Governor Brad Little mobilised the National Guard to help fight twin lightning-sparked fires that have together charred nearly 24 square miles (62 sq km) of dry timber in the remote, drought-stricken region.

The July heatwave follows unusually high temperatures in June in the West, and comes amid worsening drought conditions throughout the region.

Scientists say human-caused climate change and decades of fire suppression that increases fuel loads have aggravated fire conditions across the region.