A massive power outage plunged large swaths of San Francisco into darkness Saturday, knocking out electricity to about 130,000 homes and businesses and leaving self-driving cars stalled in city streets.

Pacific Gas and Electric Co. did not immediately say what caused blackouts to roughly one-third of the utility company’s customers in the city. Fire officials posted on X at about 3:15 p.m. that at least some of the blackouts were caused by a fire that broke out inside a PG&E substation at 8th and Mission streets.

The outage darkened large parts of the city’s north side, starting in the Richmond and Presidio neighborhoods and areas around Golden Gate Park early in the afternoon before spreading further.

Autonomous vehicles stalled in the middle of streets, triggering traffic jams across affected areas.

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The San Francisco Department of Emergency Management said on X there were "significant transit disruptions" happening citywide and urged residents to avoid nonessential travel and treat down traffic signals as four-way stops.

Waymo temporarily suspended its autonomous ride-hailing service in the wake of the blackout, SFGate reported.

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Fox News Digital reached out to Waymo for comment but did not immediately hear back.

PG&E later said that as of 11:30 p.m. Saturday, crews had restored power to about 95,000 customers, with about 35,000 customers remaining without power. The utility company added that crews would continue working through the night.

The Associated Press contributed to this report.