Authorities on Friday surrounded an elaborate, underground bunker believed to be that of a gun-toting survivalist suspected of killing his wife and daughter nearly a week ago and then holing up in the woods of Washington state.

They pumped gas into the structure in the Cascade foothills east of Seattle and heard movement inside, but the dozens of officers were not entering the bunker because they believed its occupant was heavily armed, and that it might be booby-trapped.

Sheriff’s officials said later Friday they weren’t sure the gas penetrated deep enough to reach the person inside, who they believed was 41-year-old Peter Keller. The standoff continued into Friday evening.

Sgt. Cindi West said she believed officers had opened a hatch on the bunker, so they could partially see inside. Officers had chain saws, and were contemplating trying to dismantle part of the structure, West said. No other information about what was happening at the scene was immediately available Friday evening.

Keller has not been seen since a fire at his North Bend-area home Sunday led responders to discover the bodies of his wife and daughter. The two had been shot to death.

“It’s a very extreme tactical situation,’’ King County Sheriff Steve Strachan said. “Time is on our side. We’re not going to do anything rash.’’

West said evidence found in Keller’s home helped authorities locate the bunker, dug 20 feet into the side of a ridge in an area of dense vegetation, at noon Friday. Officers were able to pinpoint the location after enhancing a blurry photograph found on a hard drive in an open safe in Keller’s house, she said. The photo included a view from the bunker in which buildings in nearby North Bend were visible, along with a set of power lines.