SAN FRANCISCO (KRON) — An explosion rattled downtown San Francisco and blew off a manhole cover Wednesday morning.

The eruption was reported in the area of 350 Bush St. shortly before 8:30 a.m., according to the fire department.

People in area heard a loud boom when it happened and smoke was initially visible.

The blast was caused by some kind of underground malfunction. The manhole cover blew off of a PG&E vault.

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 causedour equipment to fail.”

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

It may have been indirectly caused by a nearby vehicle accident, according to a utility spokeswoman.

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

No injuries have been reported.

Officials say there is no imminent threat to the surrounding area.

Fire officials reported some smoke was seen coming from the manhole but no flames.

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

Drivers should expect traffic delays in the area.Stay with KRON4 News for updates.