SAN FRANCISCO – About 21,000 homes and businesses in San Francisco were still without power Sunday morning, a day after a massive outage darkened much of the city during one of the busiest shopping weekends before Christmas, according to PG&E.

What we know:

The utility said the outage began shortly after noon Saturday in the western part of the city before spreading to several neighborhoods, including most of downtown. 

At one point, PG&E estimated that roughly one-third of all San Francisco customers were without electricity.

Investigators are now working to determine whether the outage is connected to a fire Saturday at a PG&E substation near Eighth and Mission streets.

What they’re saying:

“We do not know exactly which happened first, meaning if the fire caused the outage or not,” said San Francisco Fire Department Lt. Mariano Elias. “It’s too early to tell at this time, but in order for us to work there in a safe operation, we need the power off.”

The outage created widespread transportation disruptions throughout the city. With traffic signals dark at major intersections, drivers faced significant congestion in multiple neighborhoods. BART also temporarily closed its Powell Street and Civic Center stations due to the power failure.

The blackout also affected autonomous vehicle service in San Francisco. Waymo temporarily suspended its robotaxi operations, citing safety concerns. Video recorded during the outage showed several of the company’s vehicles stalled in intersections, at times blocking traffic and nearly causing collisions.

In a statement, Waymo said it was “focused on keeping our riders safe and ensuring emergency personnel have the clear access they need to do their work,” adding that it plans to resume service in San Francisco “soon” but did not give a specific time. 

San Francisco plunged into darkness when nearly 30 percent of the city was struck by a massive power outage on Saturday night.

Over 130,000 houses and businesses were left in the dark, largely in the northwest part of San Francisco, including the Richmond, Sunset, Presidio, and Golden Gate Park sections, officials said on Saturday. 

As of early Sunday morning, just over 36,000 people were still without power.

The “citywide” outages forced Waymo to halt its driverless car service, stranding the autonomous vehicles in the middle of the streets, SF Gate reported.

“We have temporarily suspended our ride-hailing services given the broad power outage in San Francisco,” a Waymo spokesperson told the outlet. “We are focused on keeping our riders safe and ensuring emergency personnel have the clear access they need to do their work.”

The company shut down its operation at around 8 p.m. because the cars were unable to operate without traffic signals. Residents shared footage of the Waymo vehicles parked with their hazards flashing 

At least four Waymo vehicles were parked in the middle of an intersection with their hazards on, creating a large traffic jam at the busy intersection in the North Beach neighborhood, according to video posted to X.

One passenger was left stranded inside one of the self-driving vehicles during the outage, footage obtained by the outlet showed.

A portion of the outages was blamed on a fire that broke out at a Pacific Gas and Electric substation at 8th and Mission streets in downtown San Francisco Saturday afternoon. 

The outages began as early as 9:40 a.m. Pacific Gas and Electric Co. was aware of the outages and said crews were working to restore power.

Power was restored to approximately 90,000 customers just after 10 p.m. local time, Mayor Daniel Lurie announced on X.

Crews were continuing to work on the remaining 36,000 customers on early Sunday.

“For those of you that do not have power, we want you to make sure you stay safe,” Lurie said.

The 48-year-old Democrat advised residents to check on neighbors but to remember to blow out all candles they may have been using before going to bed.

“I know there’s a lot going on out there, but people really stepped up tonight and will overnight as well,” Lurie said.

Police officer presence was ramped up in the areas without power to “ensure the safety of those still on the road,” he added.

PG&E says the grid has been stabilized, and the company is not expecting any more customers to be affected.

Rail lines and traffic signals were shut down by the outage, with city officials urging residents not to travel for the remainder of the night.

City buses had their routes changed, bypassing certain stops that were affected by the outages.

“Significant transit disruptions” were reported by the San Francisco Department of Emergency Management across the city.

With Post wires

A large power outage left almost 40,000 PG&E customers without electricity in San Francisco Saturday, according to the company.

The PG&E Outage Center first reported the outage was affecting 24,842 customers, but a few minutes later, PG&E told NBC Bay Area the outage was affecting 39,520 households in the areas of Richmond, Sunset, Presidio, Golden Gate Park and parts of downtown.

Officials warned traffic lights in these areas might be impacted and advise that if the traffic signal has gone dark, to treat it as a four-way stop.

According to the website, the outage was first reported at 10:10 a.m. and is expected to be restored at around 3:40 p.m., but PG&E told NBC Bay Area the outage started at around 1:10 p.m. and the estimated time of restoration is unknown.

This is a developing story. Details may change as more information becomes available. Stay tuned for updates.