Authorities say the official death toll from the deadly Washington state mudslide has increased to 24.

Crews searching through the muck and devastation wrought by Washington's deadly mudslide were finding more human remains on the east side of the slide, near the town of Darrington.

The Snohomish County medical examiner's office said Monday that it has received a total of 24 victims, and 17 of them have been positively identified. Previously, the official death toll was 21, with 15 victims identified.

'There's a tremendous amount of force and energy behind this.' - Steve Harris, rescue worker

Steve Harris, a division supervisor for the search effort, said Monday that search teams are learning more about the force of the March 22 slide, and that is helping them better locate victims in a debris field that is 21 metres deep in places.

"There's a tremendous amount of force and energy behind this," Harris said of the slide. He didn't provide further details.

Harris said search dogs are the primary tool for finding remains in the small, mountainside community about 88 kilometres northeast of Seattle. He said searchers are finding human remains four to six times per day. Sometimes crews only find partial remains, which makes the identification process harder.

Dozens more people remain missing, authorities said Sunday. The death toll is slowly increasing each day, as the medical examiner identifies more bodies.

Treacherous conditions

A makeshift road completed over the weekend links one side of the 121-hectare debris field to the other.

Searchers have had to contend with treacherous conditions, including household chemicals, septic tanks, gasoline and propane containers. When rescuers and dogs leave the site, they are hosed off by hazardous materials crews.

Gov. Jay Inslee on Monday asked President Barack Obama for a major disaster declaration in Snohomish County to make programs available to help individuals, households and businesses.

Last week, a federal emergency declaration was approved that provided a federal disaster team and specialized personnel to the slide area.

Members of the Seattle Seahawks football team and Seattle Sounders soccer team were scheduled to visit with community members Monday evening.