The crew, which was working on the new park in front of the Horton Plaza mall, was digging with heavy equipment when it hit a 3-inch gas line just after 8 a.m., fire officials said.
The mall was not being evacuated, but traffic was blocked in the immediate vicinity of the break.
A crew from San Diego Gas and Electric arrived at the construction site within 30 minutes. They found a valve near the site of the broken pipe and cut off the flow of gas about an hour after the rupture was reported.
Streets were reopened to traffic shortly before 9:30 a.m.