Cleanup crews returned on Monday morning to their work in Washington state where a mudslide buried a number of homes killing at least 21 people, according to the latest update by authorities.

The mudslide - after which 30 people are still missing - occurred at about noon on March 22 in Snohomish County and dammed up the Stillaguamish River, depositing millions of cubic meters of mud, tree trunks, boulders and ruins on the little town of Oso, which had just over 150 residents, and causing damage to nearby Darrington.

Jason Biermann, head of the Snohomish County Department of Emergency Management, said that the number of confirmed fatalities now stands at 21, adding that the relatively dry and sunny weather on Sunday helped emergency crews clear away several pools of water that had been complicating their efforts to recover bodies.

On Sunday, workers found another four bodies but they will not be added to the official list of fatalities until autopsies are performed on them.

Nine days after the tragedy, the missing persons list has 30 names, and Washington Gov. Jay Inslee, who visited the area, promised that the search will continue until all the victims are found and identified.

Dozens of firefighters and emergency crews, along with relatives of the victims, have been working with the help of big bulldozers and digging machines to remove the waist-deep mud and probe the ruined structures beneath with the aim of locating more bodies.

Lt. Richard Burke of the Bellevue Fire Department told the Seattle Times that the workers must wash themselves off constantly to get rid of the toxic substances - chemicals used in the home, gasoline and human waste from septic systems - that are mixed in with the mud.

"We're worried about dysentery, we're worried about tetanus, we're worried about contamination," he said. "The last thing we want to do is take any of these contaminants out of here and take them into town." EFE