Villagers in Brienz in canton Graubünden have been told to evacuate by Friday.
There are worries a large rock is to come off the mountain. Geologists believe it could be as large as two million cubic meters.
They say the rock is beginning to move so fast, it could come down any time in the next three weeks.
Local officials have issued an orange alert – which means the population can’t stay in their homes at night, livestock remain in place. Residents can be in the village during the day.
If a red alert is issued – that means no one is allowed in the village and farm animals will also be moved.
Nearby roads are already closed to the public.