Death Valley roasts in 54.4C heat in what could be highest known temperature on Earth

A nightmarish heatwave roasting America has seen Death Valley in California record what could be the highest reliably recorded temperature in history.

This year has seen heatwaves envelop areas including Canada, America and Siberia, and experts warn that computer modelling may have underestimated the impact of climate change.

In Death Valley, the US National Weather Service recorded a temperature at Furnace Creek of 54.4C, the Guardian reported.

If confirmed, this would equal a record set last year – and come close to rival figures from over a century ago, when measuring was less reliable.

Richard Rader of Scottsdale, Arizona, who said he had ridden his bike 10 miles across Death Valley on Sunday, told Reuters: ‘"I just came up here to see how hot it gets.”

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Most tourists left their air-conditioned cars only long enough to pose for pictures with the thermometer.

The National Weather Service issued excessive heat warnings across much of the region and cautioned residents that the high temperatures could be hazardous to their health, especially that of small children and the elderly.

The sweltering heat, which has extended across much of the Pacific Northwest, has pressured power grids and fueled major wildfires, including a blaze burning in southern Oregon that threatened 1,200 homes and other structures.

The Bootleg Fire, which broke out on Tuesday, had blackened 144,000 acres, or 224 square miles in and around the Fremont-Winema National Forest as of Sunday afternoon with no containment.

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Conditions at the blaze were so severe that the 926 firefighters working the lines were forced in some cases to "disengage and move to predetermined safety zones", managers said. No fatalities had been reported.

The flames were burning along a high voltage power corridor connecting Oregon’s power grid with California’s, worrying officials in both states that electricity to thousands of homes and businesses could be knocked out.

Residents in hundreds of homes were already under mandatory evacuation orders and the Klamath County Sheriffs Department said it would make arrests if necessary to keep people out of those areas.

Residents in additional parts of southern Oregon were under "Go now" orders on Sunday, while still more were told to "get set".

Watch: Extreme heat brings people to Death Valley