A heatwave is expected to send the mercury soaring to nearly 54C (130F) in California's Death Valley over the weekend – just short of the 134F reading from a century ago that stands as the highest temperature ever recorded on Earth.
Elsewhere in the US, temperatures will reach around 49C (120F) in Phoenix, Arizona, and Las Vegas, Nevada, threatening to ground aeroplanes and raising fears that pets will burn or blister their paws on scalding pavements. The heat is already so punishing that rangers took up positions at the beginnings of trails at Lake Mead, Nevada, to persuade people not to hike.
Zookeepers in Phoenix hosed down the elephants and fed tigers frozen fish snacks; Joe Arpaio, the famously hard-nosed sheriff who runs a tent jail, planned to distribute ice-cream and cold towels to inmates this weekend.
The scorching weather presented problems for airlines because high temperatures can make it more difficult for planes to take off. Hot air reduces lift and can also diminish engine performance, so planes may need longer runways or may have to shed loads to reduce weight.
Health officials warned people to be extremely careful when venturing outside. The risks include not only dehydration and heat stroke but burns from concrete and asphalt.