(SAN DIEGO) -- A single worker's error led to a massive power outage on Thursday that swept across Arizona, Southern California and Mexico, leaving millions of people in the dark and bringing major West Coast cities to a standstill, according to a local power company.
The North Gila-Hassayampa 500 kV transmission line near Yuma, Arizona 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 started to get power back to everyone, according to the San Diego Gas & Electric Co.
The outage, which started at 4 p.m. PST, appeared to stretch west from Yuma to San Diego, as far north as San Clemente, California, and as far south as the Baja peninsula in Mexico.
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.
Grocery stores across San Diego that have back-up generators were filled with people grabbing non-perishable food, water and ice. Most of the gas stations are closed, as people are being advised to use as little gas and water as possible. There were people stranded whose gas has run out, and all landline phones aren't working.
Some hospitals that usually provide urgent care were 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. And all flights out of San Diego International Airport have been suspended.
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