A massive explosion believed to have been caused by a gas line break sparked an inferno that killed at least six person and engulfed several houses in a neighbourhood near San Francisco.
The explosion, which occurred shortly after 6 pm local time on Thursday, ignited a wind-driven fire that quickly destroyed more than 170 homes, set treetops on fire and illuminated the sky for miles around.
The fire chief said he expected the toll to rise as more homes were searched.
More than 100 residents were forced to flee as the blast ripped through the town of San Bruno. About 23 people also injured in the explosion.
Hours after the explosion, fire crews from throughout the state rushed to the scene, but their efforts were hampered by violent winds, Los Angeles Times reported.
California's acting governor Abel Maldonado declared a state of emergency for the city just two miles (three kilometres) west of the San Francisco International Airport.
Local officials asked residents to register at emergency shelter. Neighbours and volunteer groups pitched in to help.
Helicopters and airplanes were seen dumping water and fire retardant chemicals in an effort to stanch the flames.
At San Francis Hospital, a major burn centre, medical crews were gearing up to treat more patients. "We do expect more victims," said spokeswoman Theresa Edison.
Meanwhile, Pacific Gas and Electric crews said that a gas line rupture sparked the explosion, spokesmen for the power company cautioned that they were still investigating. Late Thursday, the utility confirmed that one of its lines in the area had ruptured, but said that the cause of the fire had not been determined.
Doug Kunze, who lives on Claremont Drive, said he was watching a football game on television when he heard an explosion and thought it was an earthquake and saw fire. The cable went out and the water went out. "The fire was huge. It was 100 feet in the air," he said.
