Rescuers fear the death toll could rise after a gas pipeline explosion tore through a neighbourhood in San Francisco.
Four people are now confirmed dead, but emergency workers are still searching through the remains of burnt-out homes.
Some 40 properties were destroyed in the fire that followed the blast in San bruno.
The National Transportation Safety Board has begun an investigation into the cause of the explosion. An underground natural gas pipeline is reported to have been ruptured.
More than 50 people have been injured, at least three of them seriously.