Update: Nearly all PG&E customers have had their power restored at this point (just before 11 am PT), BBG reported in its latest update on the situation.
The utility said that workers from a "third-party construction company" caused the outage when they accidentally struck an underground line.
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Embattled utility PG&E reported a service interruption on Friday that cut power to 22,000 customers - about 60,000 people - in San Francisco and stranded riders on the city's Muni rail service.
One reporter said problems with PG&E Substation A had likely caused the outage, which started just before 8 am PT. The utility is hoping to have power restored by 10:30. By 9:50 PT, power had been restored to some 7,000 customers, leaving 15,000 still without power.
DEVELOPING: PG&E power outage in SF impacting some 22K customers (appx 60K people). Utility officials on scene say it’s related to problems at Substation A near the Dogpatch neighborhood. Electricity out for traffic lights and Muni subway. Power should be restored @ 10:30. pic.twitter.com/7pGXj7Wzvi— Matt Bigler (@mattbigler740) September 20, 2019
Muni service was impacted in both directions.
UPDATE: Power outage has impacted #MuniMetro rail service in the subway in both directions. We are organizing bus shuttles as quickly as possible to support svc b/t West Portal & Downtown. https://t.co/jqczl4CTlo— SFMTA (@sfmta_muni) September 20, 2019
Here's what the outage map looked like at its peak, with southeastern San Francisco the most heavily impacted:
PG&E is advising drivers to use extra caution and to treat traffic lights as four-way stops.
The utility said the cause of the outage is still under investigation.