Parts of southern California sweltered in temperatures above 100 degrees (37.7 Celsius) as a heat wave stretched into a seventh day and contributed to power outages that left thousands without air conditioning.
Southern California Edison said 20,000 customers in Los Angeles, Orange, Ventura, Riverside and San Bernardino counties had no electricity Monday.
About 9,000 more customers in scattered parts of Los Angeles also were without power, Los Angeles Department of Water and Power spokeswoman MaryAnne Piersen said.
San Diego Gas and Electric Co., which serves San Diego County and southern Orange County, declared a power emergency and began preparing for potential rolling blackouts as demand hit a record.
About 30,000 of its customers experienced outages Monday, but electricity was restored to 22,000 of them by the afternoon, spokesman Peter Hidalgo said.
"We need immediate energy conservation, or else there will be rolling blackouts," Hidalgo said.
Lightning strikes on grid equipment due to scattered desert thunderstorms added to the strain.
The California Independent System Operator, which oversees the state's power grid, said no major shortages were expected. But it was urging customers to conserve electricity by setting air conditioning thermostats higher and waiting to use major appliances until after dark.
Relief was in sight with cooler temperatures forecast over the next several days.