An extreme heatwave that has already shattered temperature records across the U.S. Southwest threatened on Friday to push power systems to the brink of failure as residents cranked up air conditioners, Reuters reported.

California power grid operators, who have so far been able to keep the lights on, issued their latest "flex alert" for Friday, asking homeowners across the state to conserve energy in the late afternoon and evening when demand surges.

The heat, which comes amid years of drought across the Southwest, has strained power grids in California and Texas and fueled the spread of wildfires.

“It feels somewhat apocalyptic with the record high heat, the smoke from wildfires tearing through the Sonoran desert and the news on the drought,” said Emily Kirkland, a communications organizer for a Phoenix nonprofit group. "Just the 10-minute walk from my house to the light rail made me queasy."

The National Weather Service has issued excessive heat warnings for five states - California, Nevada, Utah, Arizona and parts of Colorado - warning that temperatures soaring well above 100 degrees Fahrenheit (38 degrees Celsius) can be dangerous.

Temperature records have already been tied or broken in Salt Lake City, Palm Springs and elsewhere and record highs were forecast for Phoenix on Friday at 117 degrees.

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