DARRINGTON, Washington (Reuters) - The grim task of combing through debris from a landslide that sent a wall of mud cascading over dozens of homes on the outskirts of a rural Washington town came to a standstill briefly on Saturday for a moment of silence.

The sombre moment at 10:37 a.m. (1737 GMT) was observed exactly one week after the catastrophe, amid uncertainty over the fate of 90 people still listed as missing. On Friday, the unofficial body count rose to 27.

"The number is so big and it's so negative. It's hard to grasp," said volunteer Bob Michajla, 66, who has been helping to search part of the debris field that covers a square-mile (2.6 square-km). "These are all friends and neighbours and family. Everybody knows everybody in this valley."

One more body was found on Friday in the muck and rubble left after the rain-soaked hillside above the north fork of the Stillaguamish River gave way without warning on the outskirts of Oso, northeast of Seattle, a Snohomish County official said.

But that body was not included in the official death toll of 17, based on bodies found, extricated and identified by medical examiners, a process complicated by the fact that some remains have not been found intact.

Authorities have reported finding 10 more bodies in recent days but those are not included in the formal toll. Officials have repeatedly warned that the number of dead could soon rise substantially.

"Today we take a moment to forget the logistics, forget the emergency response, and forget the surge of events that have changed our community," Mayor Dan Rankin of nearby Darrington said before the moment of silence. "This moment is for them, to honour the mudslide victims, those still missing and the many grieving families."

FEARING THE WORST

An estimated 180 people lived in the path of the landslide, and authorities said on Friday they were bracing for the worst outcome for those still listed as missing, in one of the strongest official acknowledgments that many of those lives may be lost.

"We always want to hold out hope, but I think we have to at some point expect the worst," Snohomish County Executive Director Gary Haakenson told a Friday evening news conference.

"The crews are finding bodies in the field. It's a very slow process. It was miserable to begin with. As you all know, it's rained heavily the last few days. It's made the quicksand even worse," he said.

As families and friends wait for news, many have turned to social media sites to mourn and share memories of those presumed lost. A memorial page includes pleas for information on many of the missing, as well as prayers, condolences and offers of help.

"I find it difficult to do anything other than try to get updates to see if any new survivors have been found," said 50-year-old Brenda Roberson of nearby Arlington.

"My next-door neighbour lost his father and his stepmother. My daughter is friends with his granddaughter. I have other friends that have lost their entire families up there," she said.

The plight of the Spillers family has gotten much attention. Postings on memorial web pages say Billy Spillers, 30, was at home with his four children when the hillside came down on their home.

Four-year-old Jacob Spillers was pulled out alive but his sister Kaylee, 5, was found dead. Billy and his two other children are still unaccounted for. The mother was not at home and survived.

Linda McPherson, 69, a librarian, died as her husband was able to dig himself out, according to the Snohomish County Landslide Victims Memorial Page on Facebook, while a 4-month-old girl and her grandmother were among those who perished.

NO SIGNS OF LIFE

Authorities have in some cases allowed victims' relatives onto the site as the remains of loved ones are recovered, and a moment of silence is observed.

No one has been pulled alive from the rubble since the day the landslide hit, when at least eight people were injured but survived. Rescuers have found no signs of life since then.

Lifelong Darrington resident Nolan Meece, 19, a recent high school graduate and frequent presence at community meetings about the slide, said he was among the first on the pile, arriving within an hour of the disaster after getting a text from a friend.

"I was out there with my hands digging through all that mud," he said, adding that when he first arrived he heard survivors calling out but that those on the scene could not save them. "The ones I seen did not survive," he said.

But the recovery operation has shown no signs of letting up, and heavy equipment operators were working to complete a rudimentary service road for emergency workers connecting the two sides of Highway 530, which was washed out by the slide.

Ron Brown, a Snohomish County official involved in search-and-rescue operations, said the debris field may end up being the final resting place for some victims, who may be buried so thoroughly they cannot be found.

"That's going to be hallowed ground out there," he said.

John Farmer, 52, who lives east of the slide site, suggested at a community meeting on Friday that the site should never be rebuilt but turned into a park or other place of remembrance.

"A place where we can remember our loved ones, our neighbours, our families, our friends," Farmer said.