Authorities say the number of people who have been confirmed dead from the mudslide in Washington state has increased from 18 to 21.

Jason Biermann of Snohomish County Emergency Management said Sunday that 15 victims have been identified by the Snohomish County medical examiner. Six have yet to be identified.

Biermann says another four bodies were found in the debris field on Sunday.

Authorities said late Saturday that the number of people believed missing decreased substantially, from 90 to 30.

Washington Mudslide

A searcher walks down a huge pile of debris at the scene of a deadly mudslide on Saturday. (Elaine Thompson/The Associated Press)

Families coping with the loss of friends, neighbours and normalcy sought comfort in church services Sunday, as crews worked to recover more victims from the soggy pile of mud that buried the small mountainside community of Oso in Washington state, more than a week ago.

Rescue crews said Sunday that many of the dogs that have been essential in the search for victims will take a two-day break.

Days of sniffing through cold, soupy mud and nearly nonstop rain have taken their toll on the animals, and officials say dogs can lose their sensing ability if they work too long.

"The conditions on the slide field are difficult, so this is just a time to take care of the dogs," said Kris Rietmann, lead spokeswoman for the team working on the eastern portion of the slide.

Dogs from the Federal Emergency Management Agency, more recent arrivals on the scene, will continue working, said Heidi Amrine, another spokeswoman for the operation.

Engineers were watching for any material sloughing off the landslide area, making sure that a weekend of torrential rainfall doesn't displace more land.

Church service

Meanwhile, many residents attended church services for solace ahead of another week of recovery efforts.

"I can only compare it to a hot hearty meal after a very cold day," Slava Botamanenko of Darrington said of the church services.

Botamanenko works at the hospital in Arlington and said he spent two nights there to be sure he was available for work after the slide shut the road.

Authorities have said they have recovered more than two dozen bodies, but they won't be added to the official tally until a formal identification is made. And, underscoring the difficulty of identifying those killed in one of the deadliest landslides in U.S. history, Biermann said crews are not always discovering complete remains.

This weekend, crews completed a makeshift road that will link one side of the debris field to the other, significantly easing the recovery operation. They've also been working to clear mud and debris from the highway, leaving piles of gooey muck, splintered wood and housing insulation on the sides of the road.

Searchers have had to contend with treacherous conditions.

The search area has septic tanks, gasoline, propane tanks and other hazards. When rescuers and search dogs leave, they're hosed off by hazardous materials crews stationed at the edges of the debris field.

Water levels rise

The slide dammed up the North Fork of the Stillaguamish River, causing water to pool up on the east side. The river cut a new channel through the mud, but torrential weekend rainfall has raised the water level nearly 30 centimetres, Rietmann said Sunday.

In at least one place, the water level has risen so high that it's covered areas that have already been searched by Snohomish County responders, said Tim Pierce, leader of Washington Task Force 1, a search and rescue team.

"At this point there's no point in searching (that area) again until the water drops back down," Pierce said.

Rescuers should get some relief soon. Mainly dry weather is forecast Monday through Wednesday in Western Washington.

Washington mudslide search

Personnel from the Washington National Guard haved joined civilian workers in efforts to find missing persons in Oso, Washington. (Spc. Matthew Sissel/Reuters, Washington National Guard)

The size of the debris field is also smaller than initially thought, officials said Sunday. After further scientific review and analysis, geologists have determined that the size of the debris field is about 300 acres in size. That's just under half the size of the earlier projected 2.6 square kilometres.

Away from the whirring chain saws and roaring bulldozers, many residents of the nearby community of Darrington sought quiet comfort in church services.

All week, a steady stream of people has stopped in to pray at the Glad Tidings Assembly of God on the edge of town, Senior Pastor Les Hagen said.

"At a time like this, everybody knows they've got to have God's help," Hagen said.