According to a tweet by the San Francisco Department of Emergency Management, a six inch gas main break happened at the intersection of 4th and Folsom streets at about 12:35 p.m.
Moscone Center and Yerba Buena have been evacuated, as well as four surrounding buildings. Evacuees are being told to go to 756 Mission Street between 3rd and 4th streets
The San Francisco Fire Department and PG&E crews are on scene.
Traffic in the area is backed up and motorists are advised to avoid the area. No injuries have been reported.
Stay with ABC7 News for the latest on this developing story.
(Bay City News contributed to this report)