A single worker's error led to a massive power outage that swept across Arizona, Southern California and Mexico, left millions of people in the dark and brought major West Coast cities to a standstill, according to a local power company.
The North Gila-Hassayampa 500 kV transmission line near Yuma, Ariz. was tripped offline when a single APS employee was carrying out a procedure in the North Gila substation, according to Arizona Power Service.
Typically, in such an instance, the outage would be isolated to the Yuma area. The investigation is now focusing on the reason that did not occur in this case, APS said Thursday.
San Diego Gas & Electric Co. president and CEO Michael Niggli earlier said that 1.4 million affected customers could be without power through the night and into Friday.
A multi-stage restoration plan was begun to get power back to everyone, according to the San Diego Gas & Electric Co. Power reportedly was back in some areas, including Orange County, Calif.
Two million more people were reported to be without power in Mexico.
There was "no indication that this event was caused by terrorism," Niggli said earlier today, adding that the agency was working with the California Independent System Operator to bring them back online.
The outage, which started at 4 p.m. PST, appeared to stretch west from Yuma to San Diego, as far north as San Clemente, Calif., and as far south as the Baja peninsula in Mexico.
Earlier, authorities said that the outage most likely had to do with the power line that connects Arizona and California. Both major connections that bring power to the region have been disconnected.
Viewers of ABC affiliate KESQ in Palm Springs, Calif., called in to say they heard a massive explosion at a substation in Coachella. Those reports could not be immediately confirmed.
The loss of power led to a shutdown of two reactors at the San Onofre nuclear power plant. Officials from the U.S. Nuclear Regulatory Agency said it appeared to have shut down automatically at 3:38 p.m. because of the change in the power grid -- as it is designed to do, kind of like a circuit breaker. Officials are working now to reconnect the reactor so that it can help restore power to some of the many people affected.
Grocery stores across San Diego that have back-up generators are filled with people grabbing non-perishable food, water and ice. Lines are reportedly backed up everywhere.
Most of the gas stations are closed, as people are being advised to use as little gas and water as possible. There are people stranded whose gas has run out, and all landline phones aren't working.
Some hospitals that usually provide urgent care are closed, while some were under emergency lock down -- frustrating and frightening many.
Non-functioning traffic lights have caused delays everywhere, making it difficult for ambulances to get to where they needed to go.
All flights out of San Diego International Airport have been suspended, and the airport is currently running on generators.
San Diego Gas & Electric Co. also sent out a barrage of alerts on its Twitter feed, warning customers without power to "drive safety" on roads where street lights are out and "if you have a personal family emergency plan, please activate it now."
The Associated Press contributed to this report