ARLINGTON, Wash. -- Eighteen people were unaccounted for a day after a terrifying wall of mud, trees and debris destroyed as many as 30 houses in rural northwestern Washington state and killed at least three people, authorities said Sunday.
Because of the quicksand-like mud, authorities said it was too dangerous to send rescuers into the stricken area. Searchers instead flew over the one-square-mile mudslide in helicopters, looking for signs of life.
Some of the missing may have been able to get out on their own, authorities said.
Authorities were also trying to determine how to get responders on the ground safely, Snohomish County Fire District 21 Chief Travis Hots said.
Officials described the mudslide 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.
Authorities believe the slide was caused by groundwater saturation from recent heavy rainfall.
Several people -- including an infant -- were critically injured and as many as 30 houses were destroyed. One neighbourhood "is not there anymore," Hots said.
About 20 to 30 people have been displaced, Snohomish County Executive John Lovick said.
The number of missing could change because some people may have been in cars and on roads when the slide hit just before 11 a.m. Saturday, Hots said.
The mud was so thick and deep that searchers turned back late Saturday after attempting to reach an area where voices were heard crying for help.
Rescuers couldn't hear any signs of life once they got closer, and the decision was made to retreat due to safety concerns, Hots said.
Washington Gov. Jay Inslee described the scene as "a square mile of total devastation" after flying over the disaster area Sunday. He assured families that everything was being done to find their missing loved ones.
"There is a full scale, 100 per cent aggressive rescue going on right now," said Inslee, who proclaimed a state of emergency.
The slide blocked the North Fork of the Stillaguamish River. With the water rising rapidly behind the debris, authorities worried about severe downstream flooding and issued an evacuation notice Saturday.
Snohomish County officials said Sunday that residents could return home during daylight hours, but that they'll likely re-issue the evacuation order Sunday night.
John Pennington, director of Snohomish County Emergency Management Department, said there were concerns that the water could break downstream, as well as back up and flood areas upstream.
Two people were killed at the scene, and one of the people who had been rescued died at a hospital.
Shari Ireton, a spokeswoman for the Snohomish County sheriff's office, said Sunday a total of eight people were injured.
A 6-month-old boy and an 81-year-old man remained in critical condition Sunday morning at Harborview Medical Center in Seattle. Hospital spokeswoman Susan Gregg said two men, ages 37 and 58, were in serious condition, while a 25-year-old woman was upgraded to satisfactory condition.
Bruce Blacker, who lives just west of the slide, doesn't know the whereabouts of six neighbours.
"It's a very close knit community," Blacker said as he waited at an Arlington roadblock before troopers let him through. There were almost 20 homes in the neighbourhood that was destroyed, he said.
"I'm hoping for the best," Blacker said.
The American Red Cross set up at the hospital, and evacuation shelters were created at Post Middle School in Arlington and the Darrington Community Center.
Search-and-rescue help came from around the region, including the Washington State Patrol and the Army Corps of Engineers. More than 100 were at the scene.
The National Weather Service issued a flash flood watch for Snohomish County through Sunday afternoon.
People who live in the North Fork's flood plain, from the small communities of Oso to Stanwood, were urged Saturday to flee to higher ground. Even though the evacuation had been lifted Sunday morning, Inslee urged residents to remain alert.
Dane Williams, 30, who lives a few miles from the mudslide, spent Saturday night at a Red Cross shelter at an Arlington school.
He said he saw a few "pretty distraught" people at the shelter who didn't know the fate of loved ones who live in the stricken area.
"It makes me want to cry, just looking at them," Williams said Sunday.
Transportation officials said they didn't know how long the two-lane rural road would be closed.
Snohomish County authorities said the area has a history of unstable land. He said a slide also happened there in 2006.
"This slide came out of nowhere," Pennington said.
