Two manhole covers at Pier 3 blew off early Sunday morning after Pacific Gas & Electric Co. equipment failed underground, authorities said.
The Fire Department was called to the area along the Embarcadero just before 8:30 a.m.
Shannon Walsh, a barista at The Plant café at Pier 3, said she saw the incident and called police after the café lost power.
“There was just a loud noise, and basically there’s an explosion,” Walsh said. “The manhole covers blew off and a bunch of smoke came out.” The covers came to rest near the manholes, she said.
PG&E spokeswoman Jana Morris said the cause of the outage was believed to be “a failed splice” that connects two cables underground.
“It looks like there was pressure within the underground system itself, which in turn caused the two manhole covers to displace,” Morris said.
The damage caused 20 customers to lose power, which was restored at about 10 a.m., according to Morris.
The Fire Department reported no injuries.
Exploding manhole covers are not new to San Francisco.
PG&E has begun an effort to replace about 1,000 of them with new covers featuring “a spring-loaded locking system” that allows them to raise up and vent pressure coming from underground without launching into the air.
Morris said about 100 of the new covers have been installed in San Francisco so far.