Pacific Gas and Electric Company said tens of thousands of homes and businesses lost power in cities near San Francisco.
The electrical outage was reported around 7:30 a.m. Sunday in parts of Berkeley, El Cerrito, Albany, Oakland, Kensington, San Pablo and Richmond.
Bay Area Rapid Transit said its Downtown Berkeley station was closed, but was expected to reopen once generators were up and running.
PG&E said as of 9 a.m., some 50,000 customers were without power. That number dropped as the morning went on.
The utility estimated service would return around 11 a.m. for most residents.
KNTV reported the outage stemmed from an equipment failure at a substation in El Cerrito.