The bus carrying about 35 passengers was on its way from Sangla valley to Kalpa when the mishap took place.
The driver and conductor were among the dead while all seventeen injured persons have been rescued and rushed to a local hospital.
The bodies of the deceased have been retrieved and would be handed over to the family members after "an on the spot postmortem", Deputy Commissioner D D Sharma said.
Most of the deceased are from surrounding villages of Sangla and yet to be identified.
In another incident, two persons were buried alive when a huge mound of earth fell on their vehicle on Chulling-Tapri diversion road via landslide-prone Urni village.
One body has been recovered while a search is own to recover the other body as the vehicle is completely buried under huge rocks.