Dozens of people were injured and at least one person was killed when a gas explosion set an entire residential neighbourhood ablaze near San Francisco, news reports on Friday said.
A county coroner confirmed at least one fatality in the blaze, which occurred around 6 p.m. Thursday (0200 GMT Friday), CBS 5 reported.
The death toll was feared to rise as fire-workers were continuing to search for possible further victims in the smouldering rubble. Dozens of people were injured, many of them seriously, radio network KCBS said.
In all 53 houses burnt down, according to first reports. As the blaze was visible near the airport of San Francisco, witnesses initially believed that it might have been caused by a plane crash.
The blast may have been caused by an underground natural gas pipeline running through San Bruno, which is located close to San Francisco International Airport, the San Francisco Chronicle said, quoting local utility officers.
Witnesses said they heard a loud bang followed by an explosion that shook buildings and a ball of fire shooting into the sky.
"I opened my door and saw a huge fireball," Frankie Serressegue, a resident of San Bruno told the San Francisco Chronicle.
Another resident, Julio Barajas, 34, reported a strong shaking of the ground, with a huge fireball rising, the report said. He immediately took his children and drove them to safety. When he returned an hour later, the entire neighbourhood was covered in ash, he was quoted as saying.
The cause of the blast was still being investigated. According to media reports, residents had reported gas smells a day earlier.