The outage was reported at about 6:45 a.m. in the area of Spear and Harrison streets. Traffic lights were out at that intersection and police were directing cars through the area.
Power lines appeared to be tangled up in each other at a couple of points along the west side of Spear Street.
PG&E spokesman Joe Molica said crews are still trying to determine what went wrong, and are looking into whether a truck hit a power pole or a bird flew into the wires.
PG&E is replacing the damaged wires and other equipment atop the power poles in that spot, he said.
Molica said power was restored to all but three customers at about 9:15 a.m.