Eighteen US Airways flights scheduled to take off from Phoenix were cancelled on Saturday as temperatures reached 48.3 C (119 F). Planes are certified to take off for temperatures up to 47.8C (118), Todd Lechmacher, a US Airways spokesman said.

Temperatures reached 53.3C (128 F) in Death Valley, California on Sunday and Saturday, while Las Vegas hit a record high of 118F on Saturday, breaking the city’s previous high of 47.2C (117 F), according the US National Weather Service.

Concerns were also expressed for visitors to the area.

"I'm not worried as much about the people who have lived here a while," Troy Stirling, a police spokesman in Lake Havasu, Arizona near the California border, told CNN .

"It's more the tourists coming into the area, even from Southern California, who aren't used to this kind of heat".

"It's pretty dangerous... we advise everybody to avoid being outdoors," said Charlotte Dewey, a meteorologist in Phoenix.

The heat is also thought to have fuelled some of the worst wildfires in Arizona for 80 years. Nineteen fire-fighters have lost their lives battling a fire that started to the north-west of Phoenix on Friday.

The high temperatures are expected to continue in the south-west of the country, with heat warnings issued for large parts of California, Nevada and Arizona, although they are expected to drop by a couple of degrees on Wednesday.