SAN BRUNO, Calif. – A massive fire burned homes as it roared through a mostly residential neighborhood in the hills south of San Francisco on Thursday. The blaze followed a loud explosion that shot a fireball more than 1,000 feet into the air and sent frightened residents fleeing for safety.

A local fire chief said a gas line explosion likely caused the blast that sent flames tearing through the streets, incinerating possibly more than a dozen homes just after 6 p.m.

“We believe it’s a high-pressure gas line that’s blown,” San Bruno Fire Chief Dennis Haag told KPIX-TV.

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.

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

Connie Bushman returned home to find her block was on fire. She said she ran into her house looking for her 80-year-old father but could not find him. A firefighter told her he had left, but she had not been able to track him down.

“I don’t know where my father is, I don’t know where my husband is, I don’t know where to go,” Bushman said.

Victims suffering from serious burns began arriving at San Francisco Bay area hospitals shortly after the blast. An estimate of the number of injured was not immediately available. Hospitals reported receiving at least four victims in critical condition but anticipated more.

Jane Porcelli, 62, said she lives on a hill above where the fire is centered. She said she thought she heard a plane overhead with a struggling engine.

“And then you heard this bang. And everything shook except the floor, so we knew it wasn’t an earthquake,” Porcelli said.

“I feel helpless that I can’t do anything. I just gotta sit by and watch.”