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Three people were killed and eight injured in a mile-long mudslide north of Seattle that demolished at least six houses Saturday morning, blocked roads and dammed a river, bringing fears of a major flood, officials said.

“First responders heard someone inside screaming for help” as the mudslide swept a house onto a road in the community of Oso in Snohomish County at approximately 11 a.m. (2 p.m. ET) Saturday, said Washington State Patrol Trooper Mark Francis.

@SnoCoSheriff is the lead on #530slide. Another photo of initial response pic.twitter.com/PfoXASdtse — Trooper Mark Francis (@wspd7pio) March 22, 2014

Among the injured was a 6-month-old in critical condition, according to Harborview Medical Center in Seattle. The hospital was also treating a 37-year-old male and an 81-year-old man both in critical condition and a 58-year-old man and a 25-year-old woman in serious condition, said spokeswoman Susan Gregg.

Another man brought to Harborview died of his injuries, Gregg said.

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The search for survivors continued into the night. Snohomish County Fire District 21 Chief Travis Hots said at a news briefing late Saturday that people were still yelling for help, NBC station KING5 of Seattle reported.

Earlier, the search involved the Snohomish County Sheriff’s Office, Washington State Patrol, Washington Department of Transportation, and Army Corps of Engineers. The Department of Emergency Management, U.S. Navy and local fire departments were also involved in the search, the DOT said.

Portions of State Route 530 were shut down, and the monster mudslide “diverted part of a local river, which started a flood in the area,” Francis said.

"Very high potential for fast upstream, downstream flooding. Prep now in case you have to leave quickly," the Snohomish County Government warned in a tweet four hours after the initial slide.

Officials said reverse 911 calls were sent warning residents of the danger of flooding from the North Fork Stillaguamish River upstream from the slide, as well as the possibility of flooding 12 miles downstream to Arlington should there be a catastrophic breach by the river.

Snohomish County officials said in a tweet that hundreds of people could be at risk in the flood plain.

"Anyone along the flood plain of the Stillaguamish between Oso and Stanwood should leave," Gov. Jay Inslee said in a statement that offered condolences to the victims' families.

The commander of the Snohomish County Search & Rescue team told NBC affiliate KING5 that the slide is the largest he's seen in the area in 30 years.

The cause of the slide appears to be that the ground was oversaturated by heavy rainfall, the government statement said.

Francis said Snohomish County rainfall accumulations have broken records for the month of March.

Aerial photos showed a huge chunk of hillside had let loose, falling hundreds of yards into the valley.