A third-party contractor struck the 4-inch gas main at Koll Center Drive and Bernal Avenue, just east of Interstate Highway 680, at about 11:20 a.m., PG&E spokeswoman Tamar Sarkissian said.
A PG&E crew was sent to the scene to pinch the line and stop the flow of gas.
Sarkissian said the pipe was squeezed shut at 1:05 p.m. Crews remained at the scene this afternoon making permanent repairs.
Police closed Bernal Avenue between I-680 and Valley Avenue, and police said nearby businesses were evacuated.
Sarkissian said the roads were reopened at about 1:10 p.m.
She said no customers lost service because it appears that the ruptured line supplies natural gas to a business that is still under construction.