Arlington, Wash., fire Capt. Brandon Asher said people were crying out for help from underneath the rubble that cut off the small town of Darrington, Wash. At least 18 people were unaccounted for.
At least six houses were destroyed by the landslide, though that number could go up after a full assessment of the area.
Officials blamed the slide on groundwater saturation and heavy rains.
Meanwhile, the mudslide blocked the north fork of the Stillaguamish River near Oso, Wash., leading Snohomish County and National Weather Service officials to warn residents of flash-flooding downstream.
Residents who live in the floodplain downstream of the mudslide should "find another place to stay tonight," county officials said.