SAN FRANCISCO — A major power outage knocked out electricity to about 130,000 homes and businesses across San Francisco on Saturday, according to Pacific Gas and Electric Co. (PG&E).

The blackout began early Saturday afternoon, initially affecting the Richmond and Presidio neighborhoods as well as areas around Golden Gate Park, before spreading across much of the city’s northern districts.

PG&E said the outage impacted roughly one-third of its customers in San Francisco.

The utility did not immediately provide a cause for the outage. However, city fire officials said at least part of the disruption was linked to a fire inside a PG&E substation near 8th and Mission streets, reported shortly after 3:15 p.m.

The San Francisco Department of Emergency Management said the outage triggered “significant transit disruptions” and urged residents to avoid nonessential travel. Officials advised drivers to treat darkened traffic signals as four-way stops.

Public transportation was also affected. City agencies said some Muni bus routes and BART train stations were being bypassed due to the loss of power.

Social media users and local outlets reported widespread closures of restaurants and shops, along with darkened street lights and holiday decorations across multiple neighborhoods.

By about 4 p.m., PG&E said it had stabilized the power grid and did not expect additional customers to lose service. The company said it could not yet confirm when power would be fully restored. — Agencies