While John Wayne Airport resumed all commercial flights Saturday, ending a full operational stop due to a power outage, almost 12,000 Southern California Edison customers awaited efforts to restore their electricity after almost 24 hours in the dark.

As of 5:30 p.m. some 11,900 customers in the Irvine, Newport Beach and Costa Mesa area were still without power but Edison was beginning the process of reconfiguring its system to work around the damage from a substation fire and restore power to customers, Edison spokeswoman Mary Ann Milbourn said.

It was expected to continue overnight.

Customers whose power is restored may still experience brief, intermittent outages as the process continues, Milbourn said.

Traffic signals in the outage area remain dark so motorists were reminded to treat each intersection without signals as a four-way stop, she said.

Flights into and out of John Wayne Airport resumed Saturday at about 6:30 a.m., airport officials said.

The outage was reported just after 7 p.m. Friday at the airport in an unincorporated area of Orange County surrounded by Irvine, Newport Beach and Costa Mesa, and prompted all inbound commercial flights to be diverted and all outbound flights canceled.

Airport officials tweeted at 9 p.m. Friday that “All Terminal power slowly coming back online. General Aviation flights unaffected and Air Traffic Control Tower is open. The full operational stop is in effect until 7 a.m. (today). For flights departing (today), please check with your airline for more information.”

At the height of the outage, 28,028 SCE customers, mostly in Irvine and Newport Beach, were affected, according to SCE’s Lois Pitter Bruce.

“We’re working on multiple engineering solutions to resolve this incident, including ways to reduce the size of the outage,” Milbourn said. “We can’t project a restoration time at this time. Some customers may be out several days. We’re continuing to assess damage. We’re asking other customers in the area to reduce and conserve as much as they can.”

The cause of the outage was a substation fire that forced it to be de-energized. The fire has been extinguished, Pitter Bruce said. No injuries were reported.

The Orange County Fire Authority tweeted that the vault fire was near Jamboree Road and Michelson Drive.

Irvine City Councilman Anthony Kuo tweeted that about 100 residents from an apartment building on Palatine were temporarily evacuated due to smoke.

A care and reception center was set up at Northwood High School in Irvine and was available as a cooling center for those who need shelter, according to the Irvine Police Department. All city of Irvine facilities are designated cooling centers, and residents can go to cityofirvine.org for details on hours and locations.

Residents were urged to exercise caution during the outage by using flashlights and treating all intersections as four-way stops, Bruce said.

Some intersections in Irvine were affected by the outage, Irvine police reported.

“I am closely monitoring the situation with the power outage. I have been in contact with Police Chief Mike Hamel and other key staff,” Mayor Christina Shea said. “The City Council will provide whatever support is needed to our public safety officials.”

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