About 90,000 people are without power in San Francsico, the city's Department of Emergency Management said Friday afternoon.
The large power outage is affecting mostly the northern and central neighborhoods, including Pacific Heights, the Presidio, the Financial District and Fisherman's Wharf.
"We are closely coordinating with all critical facilities, including hospitals, schools, and public transportation agencies," the department said in a statement.
California Pacific Hospital and Saint Francis Hospital remain open and are using backup generators to operate, it said. New patients are being rerouted to other fully operational hospitals in the city.
Public schools are open and operating under standard blackout operating procedures.
TV affiliate KPIX reported a downtown BART station closed during rush hour; people were stranded in elevators; operating rooms were shut down; and the city's famed cable cars were halted. The power outage has also caused traffic chaos.
Fire and PG&E crews were at the site of a fire at a utility substation and vault facility on 600 Larkin St. The utility told KPIX it was the "primary source" of the outage.
Subway service disrupted in NYC
And in New York City, a power outage at a subway station halted service on several lines Friday morning.
The outage occurred about 7:30 a.m. at the station at Seventh Avenue and West 53rd Street, CNN affiliate WABC reported.
The Metropolitan Transportation Authority had generators in place there by 11:30 a.m., letting them restore power.
Some riders reported commutes up to three hours.