SAN FRANCISCO, April 21 (Xinhua) -- A power outage Friday morning left about 90,000 utility customers without electricity in the northern part of San Francisco, a city on the U.S. West Coast.

The San Francisco Fire Department notified that it received multiple emergency calls that 20 elevators were stuck with people inside when the outage took place. However, there were no injuries reported as a result.

Pacific Gas and Electric Company (PG&E) crews were seen working at the site of a smoky fire at a utility substation and vault facility,reportedly blamed by the San Francisco-based utility company to be the "primary source" of the outage.

PG&E announced that power supply for 10,000 customers had been restored before noon, and on Twitter advised people in the city to "be safe at intersections as some traffic signals may not be working."