The manhole cover blew at about 5 p.m. near the corner of Third and Mission streets, according to the San Francisco Fire Department.
No injuries were reported, but streets were closed down in the area, PG&E and fire officials said.
The fire was quickly extinguished, and PG&E was alerted to the fire at 5:14 p.m., PG&E spokesman J.D. Guidi said.
PG&E crews confirmed the fire was caused by an underground PG&E equipment failure. The fire did not cause any power outages in the area and no customers were impacted, Guidi said.
Streets in the area remain closed and there is no estimated time that they will reopen, Guidi said.
