San Bruno city officials said at a news conference Thursday night that fire crews are working to hold the fire, and the city's priority is the safety of those battling the blaze and those affected by the tragedy.
San Bruno Fire Chief Dennis Haag said he was confident that crews would be able to continue holding the fire and that it would not consume more homes.
At an earlier briefing, the fire was reported to be 50 percent contained. Cal Fire has said 53 homes were destroyed at about 120 damaged.
Haag said that a high-pressure gas line was likely to blame for the fire, but that the cause has yet to be confirmed.
The need to completely shut down gas lines is impeding firefighting efforts, Haag said, because those gas lines have residuals that need to be eliminated before crews can access the area for a search.
PG&E president Chris Johns said after the news conference that crews are currently working to stop the flow on the main gas transmission line and will then cut off the flow through the distribution lines to individual homes.
Johns said that the company would "fully cooperate" with the investigation and explore unconfirmed witness reports of the smell of gas in the area before the explosions.
Without access to the gas lines, Johns said it was too early to speculate on the cause of the explosion, although he said PG&E was unaware of any of its crews working in the area Thursday evening.
"It's a tragic event, and we really want to make sure that we can make this area safe right now," Johns said.
Johns vowed that if the investigation finds that PG&E is at fault, "We will do the right thing for those involved."
City manager Connie Jackson said that city organizations are fully mobilized to assist residents but are focusing on identifying and locating all those affected.
Jackson repeated directions for those affected to report to shelters at Veterans Memorial Recreational Center, located at the corner of Crystal Springs and Oak avenues, and at the Veterans Memorial Gym at San Bruno Park.
"It's urgently important that residents who have been evacuated or who voluntarily evacuated check in with the emergency hotline," she said. "This is our immediate priority other than the response that will continue on the scene."
San Bruno Mayor Jim Ruane, who was on hand at the briefing, said that his main concern is making sure the citizens of San Bruno are safe.
"I would ask anyone who sees this broadcast tonight to say a special prayer for those people," Ruane said.
Those affected who have made accommodations to stay with friends or neighbors are urged to register with the emergency hotline at (650) 616-7180.