Spokesman Joe Molica said PG&E received word at 10:14 a.m. that a third-party contractor had struck a plastic half-inch line while digging near Alameda de las Pulgas and Notre Dame Avenue.
Crews arrived about 12 minutes later, and the initial plan was to squeeze off the line to cut the flow of gas, he said.
However, Molica said it appears the contractor, who was using an auger to dig into the ground, struck the plastic line at the point where it branches out from a 2-inch steel line. The tool is still embedded in the line, he said.
"In situations like this, it's quicker and safer to dig holes on either side of the leak and shut the gas flow that way," he said.
Meanwhile, several nearby homes have been evacuated.
Molica said crews hoped to stop the flow of gas by 1 p.m.
He said one customer was without power, but that the number would expand to five as crews interrupted the gas flow to make permanent repairs.