Snohomish County Fire District 21 Chief Travis Hots said at a news briefing that "we suspect that people are out there, but it's far too dangerous to get responders out there on that mudflow."
Searchers in helicopters will be flying over the area of the square-mile mudslide Sunday to find people who may have been able to get out on their own, as well as look for other signs of life.
Authorities are also trying to determine how to get responders on the ground safely, Hots said, calling it as "like quicksand."
Officials described the deadly slide as "a big wall of mud and debris" that blocked about one mile of State Route 530 near the town of Oso, about 55 miles north of Seattle. It was reported about 60 feet deep in some areas.
Several people — including an infant — were critically injured and as many as 30 houses were destroyed. The slide wiped out one neighborhood, where there were about 28 to 30 homes, authorities said.
Hots said the number of missing is fluid and could change because some people may have been in cars and on roads when the slide hit just before 11 a.m. Saturday.
