Power continues to be restored to tens of thousands of San Francisco businesses and residences following a Saturday outage that affected some 130,000 customers, according to Pacific Gas & Electric Company (PG&E).

The outage was caused by a fire at an electrical substation, according to PG&E.

By Sunday morning, power had been restored to about 110,000 customers, PG&E said. The remaining 21,000 customers were located primarily in the Presidio, Richmond District, Golden Gate Park and small areas of downtown San Francisco, according to the utility.

While the damage to the substation was “significant and extensive,” there were no injures to PG&E workers or the public, PG&E said.

“The damage from the fire in our substation was extensive and the repairs and safe restoration will be complex. We will continue working until all customers are restored,” PG&E said in an early afternoon update Sunday. “We encourage customers to be safe.”

The first outages were reported at around 1 p.m. Saturday, according to PG&E, with the grid stabilized by 4:30 p.m., halting any additional outages. Fire officials brought the substation fire under control by 6 p.m., according to San Francisco ABC station KGO.

The blackout occurred when the city was teeming with tourists and holiday shoppers. The lack of power snarled traffic throughout the affected areas as traffic signals remained inoperative.

“The Saturday before Christmas is historically once of the busiest shopping days of the year,” San Francisco Board of Supervisors member Matt Dorsey told KGO. “This is the worst time that PG&E could have a problem.”

The cause of the substation fire remains under investigation, according to PG&E.