They blame overloading and over 20-year-old mechanically unfit 44-seat mini bus for the accident in which 35 other passengers received grievous injuries.
A total of 73 passengers were on board when the bus skidded off the road and fell into a deep gorge near Banjar, some 50 km from Kullu town, on Thursday. Passengers were also sitting on bus's rooftop.
Chief Minister Jai Ram Thakur visited hospitals in Kullu town, some 200 km from the state capital, to enquire about the injured and meet the families of the victims.
Thakur said a special campaign would be launched to identify and rectify the black spots on roads across the state so as to minimise accidents. New roads would allowed only after the approval by the road safety auditors.
Transport Minister Govind Thakur, who was supervising the rescue and relief operation, told over phone that some of the passengers succumbed to injuries early Friday.
Superintendent of Police Shalini Agnihotri said the private bus was on its way to Gada Gushaini from Kullu when the accident occurred.
The injured included school and college students from Banjar and were returning home.
A witness said rescuers had a tough time in extracting the victims from the vehicle and the gorge.
The spot of the accident, about 250 km from the state capital, is one of the remotest places in the state.
A bus driver, who is frequently travelling on this stretch, told reporters at the accident spot that the bus is normally overloaded with passengers.
"Since there is a scarcity of state-run bus service in most of the routes in the interior of Kullu district, people prefer to travel by private buses. The bus that met an accident was the last one on the route, so it is normally packed to capacity and travelling on bus rooftop is normal," he added.
The Kullu district administration has provided Rs 50,000 as immediate relief to the next of kin of the deceased and injured persons. A magisterial probe has been ordered.
( With inputs from IANS )