ROUGH CUT (NO REPORTER NARRATION) San Francisco Fire Department Chief Joanne Hayes-White on Wednesday said fiber optic workers in the Laurel Heights neighborhood are believed to have breached a gas line, causing a raging blaze and 'open flame' situation that triggered area evacuations.

Hayes-White said there were known fatalities after combing the scene, but told reporters it was a "very active scene" and has ordered evacuations for a one-block radius.