SAN DIEGO -- More than 2 million people on both sides of the U.S.-Mexico border were left without power Thursday after a major outage that extended from Arizona to southern California, including San Diego, the eighth largest U.S. city.
Mike Niggli, chief operating officer of San Diego Gas & Electric Co. ruled out terrorism but said the cause is unclear.
"To my knowledge this is the first time we've lost an entire system," he said at a news conference.
The outage that started shortly before 4 p.m. PDT extended from southern parts of Orange County to San Diego to Yuma, Arizona. It also is affecting cities south of the border across much of the state of northern Baja.
All outgoing flights from San Diego's Lindbergh Field were grounded and police stations were using generators to accept emergency calls across San Diego County.
Charles Coleman, a spokesman from Southern California Edison, said the two reactors at the San Onofre nuclear power plant went offline at 3:38 p.m. as they are programmed to do when there is a disturbance in the power grid, but there was no danger to the public or to workers there.
Residents in parts of eastern San Diego County and Yuma, Ariz. endured sweltering temperatures with no air conditioning.
"It's 113 degrees right now outside and 75 in my office," said Yuma city spokesman Greg Hyland, who was sitting in the dark, answering calls.
Niggli said relief was on its way, slowly. He said his 1.4 million customers may be without power until today.
He said the utility lost power due to a transmission failure that started at a large switching station in Arizona, where several high-voltage lines come together, although the cause has not been determined.
"I suspect the system was overwhelmed by too many outages in too many places," Niggli said.
In the desert heat of the Palm Springs area, the temperature was 111 on Thursday with rolling blackouts.
The Eisenhower Medical Center will serve as an oasis of air conditioning since it operates on its own power source, said hospital spokeswoman Deborah Johnson.
Johnson welcomed fragile seniors and others affected by the heat to cool off in their lobby.
"All I can say is God bless air conditioning," she said.