California has declared a state of emergency to respond to problems with the electrical system, as parts of the southwestern United States have reported dangerously high temperatures.
An excessive heat warning is in place for much of Arizona and California, and parts of southern Nevada and Utah.
People are told to stay in air-conditioned areas and out of the sun.
Californians have also been urged to conserve energy during peak hours, as temperatures are expected to stay between 100-110F (37-43C) until Sunday.
Governor Gavin Newson said the state of emergency, which is in effect until 11:59 pm Saturday (06:59 GMT Sunday), was aimed at “reducing pressure on energy infrastructure and increasing energy capacity.”
The California Independent System Operator, which controls most of the state’s electrical grid, has asked people to set thermostats to 78F (25C) or higher, to avoid using major appliances and unnecessary lights.
In California’s Death Valley National Park, generally one of the hottest places in the world, a thermometer at the Furnace Creek Visitor Center scored 130F (54C) on Thursday.
Willo Alford, who runs a general store in Death Valley Village and has lived there most of his life, told Reuters news agency: “Up to a certain temperature it’s fine, like maybe 120F ( 49C), but once it gets past when it gets really tough. “
Warmer temperatures were felt in the San Francisco Bay Area, where several cities have set up cooling centers.
In Phoenix, Arizona, temperatures hit 118F (48C) on Thursday, while Las Vegas reported 115F (46C) and Denver hit 100F (38C) for the third day in a row.
About 50 million people were subject to excessive heat warnings and heat advisories in the southwest.
A high pressure system stationed in the southwest since Tuesday caused the heatwave, a week before the official start of summer in the northern hemisphere.
The event worsens a mega-drought that has dried up rivers and reservoirs. Scientists say the west coast states of the United States should expect more from these events.
“Heat waves are getting worse in the West [Coast] because the ground is so dry “because of the region’s mega-drought,” Park Williams, a climate and fire specialist at the University of California, said as quoted by The Associated Press.
“We could have two, three, four, five of these heat waves before summer is over.”