Officials says a fire that ripped through a San Francisco suburb, ravaging scores of homes and killing at least one person, was probably caused by a natural-gas explosion.
As many as 22 people were injured by the blast and the subsequent fire in San Bruno, close to San Francisco International Airport.
Local residents say they first thought the blast's loud boom came from an earthquake or an airplane crash.
Fire Chief Dennis Haag says at least 53 homes in San Bruno are severely damaged, with a further 120 also affected.
Local utility officials are investigating whether the source of the explosion was the rupture of a large natural gas pipeline by drilling or construction work, the ABC reports.
One resident, Tina Diloia, says she heard a sound "like a low-flying plane, then all of a sudden the house shook.
"Then there was another explosion. I went outside and there was debris falling from the air."
A local pastor has told CNN he witnessed a "devastating explosion" that caused the fast-moving fire.