Officials asked everyone to stay home Thursday night and leave the roads clear for emergency personnel.
Residents were also told to conserve water as pumps didn't have electricity and that was straining the system, and to stay off their telephones, both cellular and landlines, so emergency personnel could communicate with each other. They recommended using text messages.
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Workers serve pizza to customers outside of Filippi's Pizza after a massive blackout hit Southern California September 8, 2011 in San Diego, California.
Sandy Huffaker
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Downtown is dark after a massive blackout hit Southern California September 8, 2011 in San Diego, California.
Sandy Huffaker
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People waited out traffic during the blackout at Downtown Johnny Brown's on Sept. 8, 2011.
Katie Orr
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Traffic in downtown San Diego around rush hour during the outage on Sept. 8, 2011.
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Power outages throughout San Diego County as of 9 p.m. Thursday.
KPBS
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SDFD work on getting the woman out of the elevator on Sept. 8, 2011.
Katie Orr
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Traffic backed up due to the blackout across San Diego County on Sept. 8, 2011.
Carolina Aravena
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Traffic downtown after the blackout across San Diego County on Sept. 8, 2011.
Bruticus
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Trolleys around San Diego stopped when the power went out at 3:48 p.m. on Sept. 8, 2011. The MTS said service would be restored sometime Friday, and told passengers to check schedules for buses which would be operating normally.
Jeff Filmer
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Flights were grounded at San Diego International Airport while some arriving flights were diverted to other airports during the blackout on Sept. 8, 2011.
Gatto8478
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Downtown San Diego during the massive power outage on Sept. 8, 2011.
Brad Umansky
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As the power outage on Sept. 8, 2011 went into the night, residents in San Diego relied on candlelight.
Leah S.
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A long exposure from the blackout on Sept. 8, 2011 by San Diego resident Andrew DaRe.
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Traffic on 1st Ave. in downtown San Diego right after the blackout at about 4 p.m. on Sept. 8, 2011.
Katie Orr
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Cars were all leaving downtown during the blackout.
Sole Junkie
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Trolley service was stopped when the power went out on Sept. 8, 2011. Here, a trolley near San Diego State University is stopped on the tracks.
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A Vons grocery store in La Mesa closes because of the power outage. Employees were sent home and grocery carts were lined up to keep people out.
Angela Carone
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Claudia Bateman is a resident of The Springs in La Mesa, a low income housing facility for seniors. Air conditioning went out during the blackout, and a generator powered auxiliary lighting. Bateman says she planned to spend the evening sitting by the fire entrance knitting.
Angela Carone
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The view of a darkened East County from the top of Mount Helix.
Joseph Porteous
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Shoppers pick up supplies at a 99-cent store during the blackout on Sept. 8, 2011.
Digitaria
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The night sky from University Heights during the blackout on Sept. 8, 2011.
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Neighbors and friends took advantage of the blackout to grill food and relax under the stars. Here, neighbors gather in University Heights on Sept. 8, 2011.
Andy Trimlett
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Mike Niggli, the president and chief operating officer of SDG&E, speaks at a press conference during the blackout on Sept. 8, 2011.
Erik Anderson
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Mayor Sanders speaks at a press conference on Sept. 8, 2011 during the blackout that left all of San Diego County, parts of Orange and Imperial Counties, areas in Arizona, and northwest Mexico without power.
Erik Anderson
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A family sits out on the porch during the San Diego blackout on Sept. 8, 2011.
Nathan Gibbs
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Almost the entire city was dark during the blackout on Sept. 8, 2011.
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Normal Heights during the San Diego blackout on Sept. 8, 2011.
Nathan Gibbs
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Jayne's Gastropub in San Diego is lit by candlelight during the blackout on Sept. 8, 2011.
Nathan Gibbs
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Cyclists on the road during the blackout in San Diego on Sept. 8, 2011.
Nathan Gibbs
SDG&E also asked residents to turn off air conditioners and other major appliances. Lessening the power load on the system will help officials restore power. And they also recommend unplugging small appliances.
County health officials warned residents that refrigerated food that has been at 40 degrees or higher for two hours or longer must be thrown out. It is unsafe to eat, officials said.
A boil water order for many areas of San Diego County was in place as water purification plants stopped operating. Customers in the Fallbrook, Valley Center, Helix, and Ramona water districts are asked to use “extraordinary water conservation measures.” No outdoor watering and only essential indoor use.
San Diego State University canceled all classes on Friday. Classes have also been canceled at Palomar College on Friday.
All public schools in San Diego County Schools will be closed on Friday. Managers at Grossmont Unified are required to work. Students at private schools should contact their individual schools to see if they are in session.
Scripps hospital system reports all of their hospitals are open and will reevaluate the situation Friday morning. Kaiser hospitals are also open, but their clinics are closed. The situation will be reevaluated Friday morning.
In Escondido, Palomar Hospital is open, but they have canceled all surgeries until further notice.
All employees of San Diego County and the city of San Diego are expected to report to work on Friday, officials said.
North County Transit District will decide by 2 a.m. Friday whether trains will run. If there is no train service, they will offer bus service from the stations, officials said.
The city of San Diego has opened up a public information line. The number is 619-570-1070. The county has also opened it's 2-1-1 line. Both have been experiencing heavy call volume throughout Thursday afternoon and evening.
We will update as soon as more information is available. For more immediate updates, follow the KPBS News Twitter account: @kpbsnews