California's Death Valley recorded a temperature of 53°C on Friday, making it the hottest day ever for the month of September anywhere in the world.
Extreme heat is expect to last throughout Labour Day weekend, with the National Weather Service issuing an “excessive heat warning” until September 6.
“I wish it were cooler already. This is abnormally hot for September,” Death Valley representative Abby Wines told Reuters.
California registers hottest September temperature
Ms Wines said the dry heat makes sweat evaporate almost instantly and added that people may not be aware that they are dehydrated or overheating.
Up to 120 high temperature records are expected to be broken across the western US through Wednesday, the National Weather Service said.
Soaring temperatures in California are the result of a heat dome, a high-pressure system that helps to create and ensnare heat over an area.
Studies show that extreme heatwaves are increasing in frequency due to human activity.
Pointing to climate change, California Governor Gavin Newsom declared an emergency earlier this week to increase energy production.
“All of us have been trying to outrun Mother Nature, but it’s pretty clear Mother Nature has outrun us,” Mr Newsom said.
“The reality is we’re living in an era of extremes: extreme heat, extreme drought — and with the flooding we’re experiencing around the globe.”
The state has also asked electric car owners not to charge their vehicles due to the increased risk of power cuts.
Cooling centres in Los Angeles County and other parts of the state have been set up where people can escape the heat.
Death Valley holds the record for the hottest temperature ever, reaching 56.6°C in July 1913.
The Associated Press contributed to this report
