Fire crews tried to douse the remnants of an enormous blaze and account for the residents of dozens of homes Friday after a gas line ruptured and an explosion ripped through in a neighborhood near San Francisco, killing at least four people and likely more.

Emergency workers haven't been able to get into all the homes and said there could be more casualties. Earlier Friday, officials said at least six people were killed before revising the official number to four. At least 50 people were hurt, with three suffering critical burns in the explosion Thursday evening that 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

"Now that there is daylight, there is going to be even more heartache and more difficult times ahead. Individuals are going back and seeing the devastation of this fire," said San Francisco state Sen. Leland Yee, who was at the scene.

Pacific Gas and Electric Co. President Chris Johns said Friday morning a 30-inch gas pipe ruptured about three feet underground just before 6:30 p.m Thursday, but crews still haven't been able to determine the cause of the rupture or the blast because they can't get close enough. The blaze was 75 percent contained by midmorning, fire officials said.