AlertSF sent word that a gas main break shut down occurred near Union Square. "At 2:15 today it was reported that a 10" gas main was hit by a construction crew at Mason and Post Streets. All vehicular and pedestrian traffic is being re-routed. PLEASE AVOID THE AREA."
PUC, SFFD, SFPD and PGE are all on the scene.
Update: Gas is shooting into the air, reports CBS 5, and surrounding buildings are being evacuated.
Update II: PG&E crews are working to fix the gas main, but you'll need to reroute your plans home for the evening commute. ABC 7 is streaming live footage.
Update III: Downtown SF gas main leak now capped. Shelter in place lifted. Repairs still in progress.