BONDO, SWITZERLAND (AFP) - Any hope of finding alive the eight people missing in a landslide in the Swiss Alps alive is fading, police said on Friday (Aug 25).

And it could take weeks before those who fled the area will return home, they added.

"The chances of survival are not high," said local police spokesman Roman Ruegg.

The landslide, which struck early on Wednesday, sent a torrent of rocks and mud flooding down the Piz Cengalo mountain, and into the outskirts of Bondo, a village near the Italian border.

The missing people, who come from Germany, Austria and Switzerland, were hiking in the Val Bondasca region at the time.

Police said they had set off in separate groups.

A massive search and rescue operation is underway, involving some 120 emergency workers equipped with infra-red cameras, mobile phone detectors, helicopters and rescue dogs.

According to Bregaglia mayor Anna Giagometti, paths in the area were flagged as "dangerous" earlier this month because of falling rocks. The Bregaglia municipality encompasses Bondo.

Ms Giagometti said warning signs in several languages were posted in the village.

Thick mud and sludge

Police and residents said mobile phone coverage in the area was spotty, and that could explain why those still missing had not been in touch.

But the authorities acknowledged that the chances of a happy ending were dwindling fast.

President Doris Leuthard, who examined the site from the air on Thursday, said the probability that the hikers were dead "is increasing by the hour," Blick reported.

Dramatic footage showed an entire mountainside disintegrating and unleashing an unstoppable mass of thick mud and sludge that tore up trees and demolished at least one building in its path.

Police said 12 farm buildings, including barns and stables, were destroyed, while the Graubunden canton's main southern highway was closed to traffic.

Deafening bang

"It was terrible," Ms Elisa Nunzi told Blick after witnessing the landslide from her home in a village that was located at a higher altitude.

The 27-year-old said she heard a deafening bang that sent rocks pouring down the mountain. "There were so many. It did not stop." Mr Christian Speck, the manager of a hotel in Soglio, several kilometres from Bondo, also witnessed the mountainside collapsing.

"At breakfast time, my customers and I saw rocks come lose from the mountainside and slide towards Bondo, in a huge cloud of smoke," he said.

The landslide set four million cubic m of mud and debris in motion, with its relentless mass stretching 500m across, the regional natural hazards office said.

The event was so severe that the vibrations set off seismometers across Switzerland, and measured the equivalent of a 3.0 magnitude earthquake, according to the Swiss Seismological Service.

Melting permafrost?

Experts hinted that climate change could be partially to blame for the disaster, with melting permafrost and an adjacent glacier likely destabilising the landmass.

An alert system put in place after a previous large landslide in the area in late 2011 allowed the authorities to quickly sound the alarm and evacuate around 100 people from Bondo and two Alpine cabins, amid fears of fresh landslides.

Some Bondo residents will be permitted to return home as early as Friday afternoon, Giacometti told reporters, adding though that others should expect to wait days and even weeks before it was deemed safe to go back.

Ms Simona Rauch, a Protestant minister at a church in Val Bregaglia, said residents did not expect to be gone for so long.

"People left immediately, leaving everything behind. They didn't bring anything because they thought they would be returning quickly," she said.

"No one expected this kind of catastrophe."