UPDATE: Crews restore power to most PG&E customers in SoMa

Only about 30 PG&E customers remain without power this afternoon following an equipment failure and reports of a small explosion in San Francisco's South of Market neighborhood, according to police and a PG&E spokeswoman.

About 2,400 customers lost power in the area of Second and Bryant streets shortly after 2 p.m., according to PG&E.

Police and firefighters initially said the outage was caused by a transformer failure, but PG&E spokeswoman Tamar Sarkissian later clarified that it was caused by clamps that failed. She said the clamps hold overhead wires to an insulator.

"It wasn't an explosion," Sarkissian said. "These failures can sometimes cause a noise."

At about 2:10 p.m., an ambulance was sent to 275 Brannan St., where the noise was heard and smoke was seen, but no injuries were reported, fire spokesman Deputy Chief Pat Gardner said.

Most customers had their power restored shortly after 3 p.m., Sarkissian said.

All customers should be back online by 6:30 p.m., according to PG&E.