About 16,000 San Francisco PG&E customers were still without power Sunday after a massive power outage left about a third of the city in the dark on Saturday, the utility company said.

In an update Sunday morning, PG&E said it had restored power to 110,000 customers. By the afternoon, about an additional 4,000 customers had service restored. Those without power were in the Presidio, Richmond District, Golden Gate Park and small areas within Downtown.

According to the utility company, there was a fire at one of its substations, and it caused "significant and extensive" damage.

"The repairs and safe restoration will be complex," PG&E said. "We have mobilized additional engineers and electricians."

In an update at 2 p.m., PG&E said it expects all customers affected by the substation outage to have power by 2 p.m. Monday at the latest.

"I have been in touch with community leaders in those neighborhoods and we're working to bring resources directly to those communities," Mayor Daniel Lurie said. "We will continue to push PG&E for a firm timeline on full power restoration."

The San Francisco Department of Emergency Services said PG&E would be setting up a community resource center, along with city staff, for those without power, ahead of an expected wave of heavy rain from an atmospheric river. It will be open from 5 p.m. to 10 p.m. and will be located at 251 18th Avenue, at the Richmond Rec Center.  After Sunday, it will be open from 8 a.m. to 10 p.m. daily.

Around 12:30 p.m., Lurie said he was in the Richmond district checking in with residents and local businesses, and that there was a small business outreach plan to let businesses know they can file claims with PG&E. 

"Some customers are starting to get power back with PG&E restoring power to 4,000 more homes, but there are still 17,000 customers without power. If you have a small businesses that's impacted, you can file a claim at http://pge.com/claim," Lurie said. 

At the peak of the outage, the utility company said about 130,000 customers were affected. 

Muni disruptions

Muni service along the Market Street Subway was affected due to the power outage, according to the San Francisco Municipal Transportation Agency's Muni Alerts. 

Muni riders who are affected by the service disruption can use BART for free between Embarcadero and Civic Center, BART said. 

"See a station agent to be let in," BART said.

Waymo suspends service

The autonomous driving technology company suspended its robotaxi services during the power outage.

The company announced Sunday that it was resuming its ride-hailing services. 

"While the Waymo Driver is designed to treat non-functional signals as four-way stops, the sheer scale of the outage led to instances where vehicles remained stationary longer than usual to confirm the state of the affected intersections," Waymo said. "This contributed to traffic friction during the height of the congestion."