San Bruno: California firefighters voiced hope that the death toll from a horrific inferno would not rise above four, as attention turned to what had ignited the devastating explosion.
Emergency workers said they had searched over 75 percent of the smouldering ruins left by a huge gas pipeline blast late on Thursday, which injured 52 people, including three with critical burns.
"There are holes in the ground, and some spots are still smouldering... we are going as fast as we can," said police chief Neil Telford, while fire chief Dennis Haag said he was "fairly positive" the death toll would stay at four.
Lieutenant Governor Abel Maldonado -- standing in for California Governor Arnold Schwarzenegger, who is on a trade trip to Asia -- was more cautious, stressing that a quarter of the inferno site had yet to be checked.
"I think it is still premature to say the death toll won`t rise," he said, speaking near a Red Cross emergency centre set up in a nearby shopping plaza.
A street-by-street check revealed 38 buildings were destroyed and seven others significantly damaged by the explosion and the ensuing inferno.
Local utility Pacific Gas & Electric (PG&E) said a natural gas main ruptured, but they have not been able to get close enough to the heart of the huge smouldering crater left behind to determine the reason.
"I`ve never seen anything like this," said Maldonado, who declared a state of emergency for the city just two miles (three kilometres) west of the San Francisco International Airport.
"You have a 30-inch diameter gas pipe in the middle of the road that just exploded; debris everywhere."
Federal investigators were joining local authorities to figure out the cause. "We will get to the bottom of this," Maldonado vowed. "We need to make sure this doesn`t happen again."
House Speaker Nancy Pelosi, who represents northern California, called for a thorough probe. "A full investigation must take place in the coming days to determine the cause of this horrible accident," Pelosi said.
Some area residents said they had smelled natural gas in the air during the three weeks prior to the tragedy and alerted PG&E.
Records were being checked to determine if complaints of leaking gas were made and how they were handled, said utility spokesman Jim Smith.
The neighbourhood was being treated like a crime scene, with police restricting access. One man was arrested for alleged looting, a spokesman said.
The massive explosion and inferno ripped through a neighbourhood in San Bruno near San Francisco early Thursday evening, leaving residents shocked by the sudden devastation.