The break was reported at 1:13 p.m. in the 600 block of San Benito Street, near downtown, PG&E spokesman Jason King said.
King said the rupture was caused by a third party, and that two PG&E customers were left without gas service.
Repair crews responded and pinched off the pipe, stopping the flow of gas, at about 2:30 p.m., King said.
Final repairs were expected to be completed by the late afternoon and PG&E personnel assisted the affected customers in relighting their pilot lights, he said.
The gas leak did not result in any evacuations, King said.
PG&E is reminding Bay Area residents to call 811 before doing any digging to learn the location of underground gas lines.