A massive fire burned homes as it roared through a mostly residential neighborhood in the hills south of San Francisco following a loud explosion that shot a fireball more than 1,000 feet into the air and sent frightened residents fleeing for safety, witnesses said.

PG&E submitted paperwork to regulators that said a section of the same gas line -- about two and half miles from the blast -- was within "the top 100 highest risk line sections" in the utility's service territory.