UPDATE: PG&E has acknowledged that a company gas transmission line was ruptured prior to Thursday night's explosion and fire in San Bruno.
"Though a cause has yet to be determined, we know that a PG&E gas transmission line was ruptured," the company said in a statement. "If it is ultimately determined that we were responsible for the cause of the incident, we will take accountability."
At least two dozen people were injured and one person was killed in the 6:30 p.m. explosion that shook the ground and sent flames ripping from house to house in the Crestmoor Canyon area. A local state of emergency has been declared.
Multiple burn victims of all ages were being treated at Kaiser in South City and at hospitals in Millbrae and San Mateo. Some were taken to a burn center in San Francisco and to San Francisco General.
Jose Alvarado, who lives on Glenview Drive, said he heard an explosion and tried to open his front door, but the flames drove him back inside, where the force of the blast had shattered his windows.
He said he grabbed his roommate and the two fled out the back door, the flames at their backs, and kicked down a fence to escape.
He was not hurt, but his roommate, who was burned, was taken by ambulance to a hospital.
One girl, 14, who was at San Francisco General Hospital, said she escaped from her home with her parents, who are in their 60s, by running through their back yard and scaling an 8-foot fence.
San Bruno resident Maureen Hartje, who lives about a block away from the blast, said she was on her deck when she heard something that sounded like "the Blue Angels were flying over."
She then saw white smoke, which turned black.
The incident was initially reported as a plane crash, but soon the investigation turned to a gas leak. Witnesses said the blast shook the ground so hard they thought it was an earthquake.
The fire started near which was not damaged.
Patch reporters are at the scene, and we will update this story as more details become available.
If you have photos or video from the fire, please post them to this story.
South San Francisco Patch editor Drew Himmelstein contributed to this report.