Himachal Transport Minister GS Bali said that at least 50 are feared to have washed away.
Following the incident, the National Highway 21 from Mandi to Aut has been closed due to the threat of landslides.
"The army and NDRF have been called while police, home guard and fire services have already been deployed in the rescue and relief operation", Kadam said.
So far, eight bodies have been recovered from the debris.
One of the state roadways bus was hit by the landslide debris and skidded off the road, falling down by nearly a kilometre. The police said the two buses were parked on the highway while the passengers were out for snacks just before the landslide happened. It swept away the buses 800 metres down into a gorge and buried one of the buses completely.
One of the buses was on its way from Chamba to Manali and the other from Manali to Katra. People present on the spot said the rescue operation was affected by rains. They believe 35-50 passengers were on the bus at the time of the incident.
Local TV channels reported that the two buses were stationed at a roadside eatery located on the highway for refreshments when the disaster occurred.