Last Updated Mar 23, 2014 7:30 AM EDT
SEATTLE - Rescue crews searched into the night for survivors from a massive mudslide in Washington state that killed at least three people, after hearing voices from the debris field pleading for help.
The slide of mud, trees and rocks happened about 11 a.m. Saturday morning. Several people - including an infant - were critically injured and at least six houses were destroyed.
Snohomish County Fire District 21 Chief Travis Hots said at a news briefing late Saturday that searchers weren't giving up on finding more people.
"We have people who are yelling for our help, and we are going to take extreme risks," Hots said.
It wasn't clear how many people might still be alive, he said.
"This is still a rescue mission until we determine otherwise," Hots said.
The slide also blocked the North Fork of the Stillaguamish River, which prompted an evacuation notice because water was rising rapidly behind the debris. Authorities worried about severe downstream flooding if water suddenly broke through the blockage.
The landslide also completely covered State Route 530 near the town of Oso, about 55 miles north of Seattle. It was at least 135 feet wide and 180 feet deep and hit just before 11 a.m., Snohomish County authorities said.
The Snohomish County sheriff's office reported that two people had been killed at the scene. Authorities later said one of the people who was rescued died at a hospital.
The injured included a 6-month-old boy, who was in critical condition at Harborview Medical Center in Seattle.
Hospital spokeswoman Susan Gregg said two other victims were in critical condition - an 81-year-old man and a 58-year-old man - while a 37-year-old man was in serious condition. Gregg said Harborview had one other male patient from the landslide, but no information on his condition was available.
Five of the injured were brought to Cascade Valley Hospital in Arlington, and one has already been treated and released, said hospital spokeswoman Jennifer Egger. She didn't know the condition of the others.
The American Red Cross has set up at the hospital, and an evacuation shelter was created at Post Middle School in Arlington.
One eyewitness told the Daily Herald that he was driving on the roadway and had to quickly brake to avoid the mudslide.
"I just saw the darkness coming across the road. Everything was gone in three seconds," Paulo Falcao told the newspaper.
Search-and-rescue help came from around the region, plus the Washington State Patrol and the Army Corps of Engineers.
Authorities believe the slide was caused by ground water saturation from recent heavy rainfall.
The National Weather Service has 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 to flee to higher ground.
Forecasters warned that some flooding was also possible north of the slide area. The Weather Service said "catastrophic flooding" was unlikely downstream, but authorities were taking no chances and urged people to leave.
Bart Treece, spokesman for the Washington State Department of Transportation, said he didn't know how long the two-lane rural road will be closed. Drivers were advised to find another way to get between Darrington and Arlington, he said.
"We're standing by ready to help out where we can," Treece said.