ARLINGTON, Wash. (AP) -- Looking for any signs of life in the quicksand-like mud below, searchers in helicopters scanned a huge debris field Sunday trying to find 18 people still unaccounted for following a deadly landslide that ripped through homes and blocked a river, threatening flooding, in rural northwestern Washington state.
Rescuers' hopes of finding more survivors were buoyed late Saturday when they heard people yelling for help from within the debris field, but they were unable to reach anyone.
The mud that killed at least three people and destroyed as many as 30 homes was so thick and deep that searchers had to turn back.
Rescuers couldn't hear any signs of life once they got closer, and the decision was made to retreat because it was too dangerous, Snohomish County Fire District 21 Chief Travis Hots said Sunday.
"We have this huge square-mile mudflow that's basically like quicksand, it's extremely fluid," he said.
The slide wiped through a grouping of homes nestled by the hills and trees. One neighborhood "is not there anymore," Hots said.
Because of the unstable situation, authorities said it was too dangerous to send rescuers into the area Sunday, so searchers took to the sky above the 1-square-mile mudslide.
Some of the missing may have been able to get out on their own, authorities 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.
Officials described the mudslide as "a big wall of mud and debris." It blocked about a 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 ground water saturation from recent heavy rainfall.
Several people - including an infant - were critically injured. About 20 to 30 people have been displaced, County Executive John Lovick 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 percent 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 downstream flooding and issued an evacuation notice Saturday. The water had begun to seep through the blockage Sunday afternoon.
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.
Shari Ireton, a spokeswoman for the Snohomish County sheriff's office, said Sunday that 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 neighbors.
"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 neighborhood that was destroyed, he said.
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.
Evacuation shelters were created at Post Middle School in Arlington and the Darrington Community Center.
Dane Williams, 30, who lives a few miles from the mudslide, spent Saturday night at a Red Cross shelter at the 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," Williams said Sunday.