The bus was on way from Rekong Peo to Rampur town when the accident occurred near Nathpa.
At least 18 people were killed and 12 others injured on Tuesday after a private bus rolled down a 200-metre gorge in Himachal Pradesh's Kinnaur district ahead of Rampur, police said.
The toll could increase, officials warned.
The bus was on its way from Rekong Peo to Rampur town when the accident occurred near Nathpa, some 180 km from Shimla. Superintendent of Police Rahul Nath told IANS over the phone that the bus skidded off the road.