Update at 8:20 a.m. ET, Sept. 9. San Diego Gas & Electric reports on its Twitter page that:
"VP of @SDGE says after a long but productive 12 hours we have restored power to nearly all 1.4 million of our customers."
Update at 6:45 a.m. ET, Sept. 9
"Power is beginning to return to pockets of San Diego County after electricity was cut to millions due to human error at a power line switching station in Arizona," our colleagues at KPBS report.
But huge problems remain, as The San Diego Union-Tribune says:
"An unprecedented power outage led to controlled chaos Thursday throughout San Diego County and surrounding areas as up to 5 million people coped with the sudden loss of electricity, and officials said power would be restored in waves through Saturday."
The cause of the outage has been traced to work that was being done at a power substation in Arizona. A utility there, Arizona Public Service, says in a statement that:
"At approximately 3:30 pm today, the North Gila — Hassayampa 500 kV transmission line near Yuma, Ariz., tripped off line resulting in a major power outage across southwest Arizona and into Southern California. Among APS customers, approximately 56,000 lost service throughout Yuma, Somerton, San Luis and Gadsden. APS is in the process of restoring service to customers in these communities.
"The outage appears to be related to a procedure an APS employee was carrying out in the North Gila substation, which is located northeast of Yuma. Operating and protection protocols typically would have isolated the resulting outage to the Yuma area. The reason that did not occur in this case will be the focal point of the investigation into the event, which already is under way."
The Union-Tribune adds that:
"The power failure led to school and business closures, suspended water service in some areas, flight cancellations, blacked-out traffic lights, silent radio stations and trapped elevator passengers. Public schools throughout the county and several high-education institutions will be closed Friday."
Our original post — 'Massive' Power Outage In San Diego, Points East:
"A massive power outage struck Southern California at about 3:38 PM [local time], affecting millions of people in the region," our colleagues at KPBS report. "There are numerous reports of people stuck in elevators, the loss of traffic signals throughout the region and serious confusion."
San Diego Gas & Electric says "all 1.4 million of our customers are currently without power" and that "the outage seems to have originated in Arizona. This caused our line from AZ and from the north of our region to both trip off."
The San Diego Union-Tribune reports the outage "has spread across San Diego County and the West, from south of the Mexican border to Orange County and east to Arizona."
KPBS will be following the story.
Update at 9:40 p.m. ET. 2 Million Without Power:
It's now estimated that "more than 2 million customers "on both sides of the U.S.-Mexico border" are without power, The Associated Press says.
Update at 9:10 p.m. ET. On The Cause:
San Diego 6 News reports that Mike Niggli, president and chief operating officer for San Diego Gas & Electric, "confirms that the power outage was not the result of a terror attack."
And The San Diego Union-Tribune reports that Niggli:
"Said the massive, unprecedented outage was due to cascading events that began first when a transmission line in Arizona went out that then knocked the San Onofre nuclear power plant offline.
" 'Essentially we have two connections to the rest of the world — one to the north and one to the east — and both of those connections were severed,' he said. 'We actually don't know what happened to the line. All we know is the line went out.' "
Update at 8:45 p.m. ET: The power company just advised customers that "if you have a personal family emergency plan, please activate it now."
KPBS says "some customers may be out for days" and that "officials do not know the cause at this time, but do not believe it is related to terrorism."