A search and rescue operation is on involving local authorities, the Army and the National Disaster Response Force.
One of the state roadways bus was hit by the landslide debris and skidded off the road, falling down by nearly a kilometre.
According to eyewitnesses, the two buses were stationed at a kiosk located on the highway for refreshments when the disaster occurred.
A bus and other vehicles are feared trapped in the debris.
Director General of Police Somesh Goyal said that as per preliminary information there were eight passengers in the Manali-Katra Volvo bus while 47 passengers were travelling in the other bus.
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Mangled remains of the bus bound for Katra in Jammu were retrieved.
The death toll is likely to increase, said the official.
The number of passengers in the buses could be between 30 and 40 as the number of passengers who boarded the bus en route was not known. It swept away the buses 800 metres down into a gorge and buried one of the buses completely.
"The exact number of missing persons is yet to be assessed".
Chief Minister Virbhadra Singh and Leader of Opposition Prem Kumar Dhumal rushed to the spot.