An explosion and fire in San Francisco has led authorities to advise residents to stay indoors

An underground explosion in San Francisco’s Tenderloin neighborhood has prompted fire officials to issue a shelter-in-place warning this afternoon because of toxic smoke caused by an underground explosion and fire.

About 4,500 Pacific Gas and Electric customers lost power shortly after 11:30 a.m., when an underground explosion occurred in the area of Polk and O’Farrell streets.

Firefighters used CO2 to suppress the flames, but PG&E requested they stop using it in order to allow the equipment to fail completely, fire Lt. Mindy Talmadge said.

But when firefighters stopped using the CO2, a black cloud of smoke seven stories high rose from the manhole. At one point around 1:15 p.m., flames 10 feet high shot from the manhole.

The downtown area has been seriously impacted as buildings with smoke detectors automatically have shutdown systems including elevators.