The National Weather Service has issued an excessive heat warning for much of the southwestern United States, as temperatures climb to near-record levels.
Forecasters say the thermometer could hit 54 degrees Celsius in Death Valley, California. Death Valley is the site of the hottest temperature ever recorded on Earth - 57 degrees Celsius in 1913.
Authorities in such large cities as Phoenix and Las Vegas say the weather could be life-threatening for those at the highest risk, including children and the elderly.
They urge everyone to take precautions, such as limiting outdoor work, wearing loose-fitting clothing, and drinking plenty of water.
Meteorologists blame the extreme temperatures on a massive high pressure system trapping desert heat.