Apparent underground vault explosion in downtown San Francisco

SAN FRANCISCO - An incident that sent a PG&E manhole cover flying this morning in San Francisco's Financial District may have been indirectly caused by a nearby vehicle accident, according to a utility spokeswoman.

The manhole cover blew off a PG&E vault in the area of 350 Bush St. shortly before 8:30 a.m., according to fire officials.

PG&E crews are investigating, but spokeswoman Andrea Minniti said it appears that a vehicle accident may have been to blame.

"The fire department reported that a car hit a fire hydrant probably half a block away," Minniti said. "Because of that crash, some water was sent downhill and leaked into PG&E underground equipment, which caused
our equipment to fail."

It remains unclear exactly what caused the manhole cover to blow off or what damage might have occurred in the vault.   

No power outages were reported in the area.

Fire officials reported some smoke was seen coming from the manhole but no flames. No injuries have been reported.

Minniti said PG&E crews will remain on scene until later this morning, but are only blocking one lane so traffic impacts should be minimal.

Twitter users say they heard a loud explosion in the area.