A huge electricity outage hit San Francisco on Saturday, leaving 130,000 residents without power and prompting city authorities to ask residents to stay home, according to the utility provider and the mayor.

Large parts of the West Coast tech hub, which has a population of more than 800,000 people, were plunged into darkness with disruptions to public transport and many traffic lights not working on a busy Christmas shopping weekend.

"We are working with first responders and city officials on an outage in San Francisco affecting approximately 130,000 customers," said Pacific Gas & Electric Company, the city's main power provider, in a statement on X.

A spokeswoman for the company said in a video posted on social media that crews were working to fix the problem.

"We do expect restorations later this evening," she said.

Parts of the city were blanketed in fog and many businesses were forced to close for the day at the height of the holiday shopping period, the San Francisco Chronicle newspaper reported, leaving normally bustling commercial areas quiet.

The city's mayor told residents to stay off roads if possible, adding some traffic signals were out and authorities had sent police and traffic officers to manage intersections. 

"But we've got rain coming, it's night time. If you don't need to go out, stay home and I'll keep you posted," Mayor Daniel Lurie said at the city's emergency operations center in a video posted on X. 

A fire at a substation had caused the blackout, Lurie added, saying it was not clear when power would be completely restored.