“In the region of Val Bondasca, eight people who were there at the time of the landslide have not been found,” Graubünden cantonal police said in a statement.
Six of them were reported missing by relatives.
The landslide happened on the Piz Cengalo, producing a wave of rubble and mud that travelled down the Bondasca valley.
The events triggered the area's rockfall alarm system – installed after a previous huge rockfall in 2012 – meaning before the debris approached the village of Bondo the fire service was able to evacuate its inhabitants, as well as people staying at two Swiss Alpine Club cabins nearby.
However on Thursday morning they said search teams, assisted by a helicopter, had been looking through the night for the eight missing people.
“There are often hikers in the affected area,” Graubunden police spokesman Markus Walser told Blick, adding that the area did not have mobile phone reception.
“We hope this is the reason we have not been able to reach the people believed to be in the area,” he added.
Images showed an unstoppable mass of thick mud and sludge moving down the mountainside like lava, ripping apart at least one building in its path and partially engulfing others.
A broad swathe of farmland was covered in a grey, moving mass.
Police said 12 farm buildings, including barns and stables, had been destroyed by the flow of debris, while Graubunden's main southern highway, linking Stampa to Castasegna, was closed to traffic.
The following video shows the rockfall on the Piz Cengalo.