Published: Sep 10, 2010 8:30 AM EDT
Updated: Sep 10, 2010 5:29 AM EDT

SAN BRUNO, Calif. (AP) - Fire crews sifted through dozens of burned-out houses and tried to account for the residents Friday after a gas line ruptured and a massive fireball exploded through a neighborhood near San Francisco, killing at least four people.

Crews with dogs went house to house and officials said there could be more casualties from the Thursday evening blast. Homes were left with just chimneys standing and smoke still rose from 15 acres of smoldering wreckage. Fire officials said the blaze is fully contained, but a quarter of the homes are still too hot to search.

"It was pretty devastating," said San Bruno Fire Chief Dennis Haag. "It looks like a moonscape in some areas."

Eight investigators were at the scene Friday, working to determine the cause of the explosion. Police are blocking people from approaching the burn area.

"Until we can determine what caused that, we are protecting that like a crime scene, looking for evidentiary value items," said San Bruno Police Chief Neil Telford.

One man was arrested Thursday night on suspicion of looting and assaulting an officer, Telford said.

At least 50 people were hurt in the blast and fire, with eight in critical condition at area hospitals. The explosion left a giant crater and sent flames tearing through the middle-class neighborhood of 1960s-era homes in hills overlooking San Francisco, the bay and the airport.