The exercise, which began at 10:30 a.m., involved the evacuation of between 3,000 and 4,000 employees and others at a number of buildings around Civic Center Plaza, organizers said.
The buildings included City Hall, the University of California at Hastings College of the Law, the Federal Building on Golden Gate Avenue, the San Francisco Main Library and the War Memorial complex.
Fire alarms were being activated, and evacuees were being directed to Civic Center Plaza, the War Memorial complex area at McAllister Street and Van Ness Avenue, and UN Plaza, according to the San Francisco General Services Agency, which is organizing the event.
The exercise is intended to allow emergency responders to assess and fine-tune their practices.
