A gas explosion started a major fire in a San Francisco Bay Area neighborhood on Thursday, damaging several homes and sending heavy smoke into the air.

Local fire officials told KGO-TV that at least six people were transported to the hospital.

A spokesperson with Pacific Gas & Electric Co. said a construction crew damaged an underground gas line around 7:35 a.m. The company said it was not their workers.

Utility workers isolated the damaged line and stopped the flow of gas at 9:25 a.m., PG&E said. The explosion occurred shortly afterward.