A transformer blew around the Van Ness station at about 5:45 p.m. leading to the outage, Muni spokesman Paul Rose said. He said Muni crews are working with PG&E to restore service as quickly as possible.
No estimated time of restoration has been announced, however bus shuttles are available for stranded Muni passengers between the Embarcadero and West Portal stations.
Rose recommend commuters check Twitter for updates.
The outage is unrelated to an earlier incident where a wheelchair-bound woman was hit by an F-train near the corner of Church and Market streets.
That woman was transported to a hospital but the severity of her injuries is not known.