According to San Diego Gas & Electric Co., power is being restored in pockets of the community. Officials said about 325,000 customers have been restored of the 1.4 million SDG&E serves.
As for Southern California Edison, about 500 to 2000 customers were without power, and about 117 customers have been restored.
SDG&E Officials say the system is coming back in pieces and a steady advance should be seen by 2 a.m. through midday Friday. However some may not have power until Saturday.
All public schools in San Diego County as well as the Capistrano Unified School District will be closed on Friday.
Arizona Public Service Co. officials have confirmed that an employee removing a piece of monitoring equipment that was causing problems likely caused a massive outage. They would not say whether it was mistake or how much experience the employee had.
The outage that started shortly before 4 p.m. PT extended from southern parts of Orange County to San Diego to Yuma, Arizona. It also was affecting Riverside County, including the Coachella Valley, and cities south of the border across much of the state of northern Baja, Mexico.
SDG&E Darcel Hulce said during a press conference Thursday that the outage was not the result of a terror attack.
SDG&E said the outage was affecting all of its customers. San Diego bore the brunt of the blackout -- with power out from Chula Vista to Oceanside, and as far east as Alpine. Officials in San Diego say 13 police stations are without power, but they are taking emergency calls by using generators.
SDG&E 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.
Several sewage pumps and water pump stations failed throughout San Diego. Raw sewage leaks were reported in several areas and boil water notices have been going out to affected residents.
Officials are trying to contact residents who are on life support. If not reached, they said they will go door to door to make sure they're okay.
Shortly before 8 p.m., the utility said crews were beginning to restore the transmission system -- the power line that runs from central Arizona to California, which experienced the initial problems, had been re-energized, as well as the connection from San Onofre to Oceanside.
The California Independent System Operator, which manages the state's power grid, issued a transmission emergency.
San Diego State University has canceled classes Thursday night and all flights out of San Diego International Airport have been grounded. Trains and trolleys have suspended service to and from the San Diego area.
Some SoCal Edison customers in south Orange County and Riverside County were also without power Thursday night. In Orange County, outages were confirmed in San Clemente, San Juan Capistrano, Laguna Hills, Laguna Niguel, Dana Point, Mission Viejo, Ladera Ranch and Coto de Caza.
By 8:30 p.m. power had been restored to some sections of Orange County, but the areas were not specified. Officials said power was expected to remain out overnight, with service restored throughout the day Friday.
Charles Coleman, a spokesman for 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 at the plant.
Los Angeles Department of Water and Power customers are not being affected.
For more information regarding the power outage, check SDG&E's website at www.sdge.com.
DEVELOPING... We will add more details to this report as they become available.
The Associated Press contributed to this report.