Bay Area Fire: San Bruno Explosion, Fire: Twitter Alerts, Video,

We believe it's a high-pressure gas line that's blown," San Bruno Fire Chief Dennis Haag said.

Pacific Gas and Electric, the utility company that serves the San Francisco Bay area, had crews in the area investigating the possibility of a natural gas explosion but had no additional information, said spokesman J.D. Guidi.

Following the initial blast, flames reached as high as 60 feet in the air as the fire fueled itself on burning homes. Planes and helicopters flew over the neighborhood dumping water in an effort to stanch the flames.

Local residents said they felt an explosion followed by a fireball that soared hundreds of feet into the air.

“We heard what sounded like a plane, then all of a sudden an explosion,” Carmann Robbins told KTVU. “It shook the window. It kind of startled me. We jumped up and then all you could see was flames. The flames were just spreading all through the houses. I don’t think the people had time to get out. It (the fire) was jumping from one house to one house to another.”

Judy and Frank Serrsseque were walking down a hill away from the flames with a makeshift wagon carrying important documents, medication and three cats.

Judy Serrsseque said she heard an explosion, saw that fire was headed toward their home and knew they had to leave. As they fled, they said they saw people burned and people struggling to get their things out of burning houses. "We got everything together, and we just got out," Judy Serrsseque. "Mostly we're wondering if we have a house to go back to."