The death toll in the devastating landslide in the US state of Washington is expected to rise “substantially” in the next day or two, an official says.

The confirmed number of dead stands at 16 with at least eight more bodies believed located, and there are 90 listed as missing after the monster mudslide crashed onto the town of Oso.

But Snohomish County district fire chief Travis Hots said bodies were not being included in the official death toll until they had been recovered and “medical officers have done their difficult work”.

“You’re going to see these numbers increase substantially” in the next 24-48 hours, he told reporters.

A total of 49 dwellings in the rural town were hit by the 2.5 square kilometre wall of mud, rocks and trees, which also destroyed part of a highway some 95 kilometres northeast of Seattle.

Over 200 rescue workers have been working in grim conditions for the last five days.

A few survivors were found immediately after the mudslide, but none since Saturday.

Fire chief Hots said they have not given up hope of finding survivors, even if the chances diminish by the day.

“If we find one more person alive, to me that’s worth it,” he said.

He described workers recovering a victim on Wednesday from a car which had been swept 200 feet from the highway, in a process that took several hours

“What happens is, when the person is removed, things kinda get sombre out there. It gets really quiet for a few minutes. You can almost hear a pin drop,” he said.

“You see seasoned veterans in this business, they start to tear up, their eyes get glossy. It’s kinda their way of paying respects to these people’s loved ones.”

Questions over landslide danger

The updated figures came as managers defended their record, noting that experts had warned of the landslide risk four years ago.

They pointed to a 2010 report commissioned after a major landslide in 2006 pinpointed the hillside overlooking Oso as among the most dangerous in terms of possible collapse.

Townspeople “knew the risk, but they felt safe in the small events”, Snohomish County emergency management chief John Pennington told reporters.

“This wasn’t a small event. It was large, it was very catastrophic,” he added, at one point fighting back tears.

Frustrated locals blocked from search

While the official recovery operation cranked into higher gear with 200 workers attacking the landslide area from both sides, there were signs of frustration from some locals.

Speaking in Darrington, one of the nearest towns, resident Kraig Wenrick said people in the local community were being told they could not help despite knowing the local area intimately.

“It’s tearing us apart,” he told AFP. “Everybody’s upset about it because they need to just get down there and let us do our job. We know this community, we know the housing down there, we know where everybody lived.

“We know this area better than anybody, and to have people come in here who don’t know nothing, and try to tell us how to do this, just isn’t acceptable,” he said.