The incident was reported to the Sunnyvale Department of Public Safety at 12:02 p.m., a dispatcher said.
The 1-inch plastic gas line ruptured at 1235 Reamwood Ave., PG&E spokesman JD Guidi said. It was originally believed to have been a 4-inch service line.
It was reported to PG&E at about 12:15 p.m. and officials from the company were onsite working on the leak before 1 p.m. The leaking gas was expected to be stopped by 2 p.m.
It may take until at least 5 p.m. for the two PG&E customers who were without gas to have their service restored, he said.
The break was caused by a construction crew working nearby, Guidi said.