SAN FRANCISCO, Calif. -- A conduit fire at the Macy's building in San Francisco's Union Square prompted an evacuation of patrons and employees Monday afternoon, a fire lieutenant said.

Employees reported hearing an explosion in the building at 170 OFarrell St. at about 12:30 p.m., said San Francisco fire Lt. Mindy Talmadge.

Firefighters located the fire in the roof area of the building and quickly extinguished it, Talmadge said.

Customers and employees left the structure in accordance with the building's evacuation plan and remained evacuated as of 12:50 p.m.

Pacific Gas and Electric Co. is responding to investigate the cause of the fire.