The break occurred shortly after 10 a.m. in the 400 block of Wiget Lane, where Kaiser Permanente's Park Shadelands medical offices are located.
"There was a concern that there might be some gas in the building, so they shut off the power to the building," Contra Costa County Fire Protection District spokeswoman Emily Hopkins said.
One of the Kaiser buildings that was evacuated contained pediatric and women's health offices; the other contained eye care and physical therapy offices, PG&E spokeswoman Tamar Sarkissian said.
Kaiser Permanente spokesman Jim Caroompas said all of the buildings are outpatient facilities.
The PG&E building that was evacuated was an administrative office, Sarkissian said.
Sarkissian said at about 1 p.m. that the gas leak had been stopped and evacuation orders were in the process of being lifted. She said the main that had ruptured was a one-inch line.
"We were able to pinch the line," she said.
Repairs were under way and were expected to be completed shortly.
Caroompas said that although the buildings are being reopened, patients who have appointments this afternoon should call before they show up.