Two buses carrying more than 60 people were swept by a landslide into a rain-swollen river in Nepal, with three survivors rescued after swimming to safety.

The vehicles, carrying at least 65 people between them, were swept off the Narayanghat-Mugling highway near Simaltar, about 120km (75 miles) west of the capital, Kathmandu, early on Friday.

Government administrator Khima Nanada Bhusal said the three survivors, who reportedly jumped into the Trishuli river and swam to the banks, were taken by residents to a nearby hospital, where they are now being treated.

Authorities mobilised the military and police to search for the missing passengers but the continuous rain was making rescue efforts difficult with landslides blocking the route leading to the area in several places, said Bhusal.

Police spokesman Dan Bahadur Karki said there were 41 people in the first bus travelling from Kathmandu to Gaur, while the second from Birgunj to Kathmandu had 24 passengers. It is thought that more may have boarded en route.

Dozens have died in the Himalayan nation since the middle of June as torrential monsoon rains triggered landslides and flooding.

A bus was knocked by a landslide on the same highway, killing the driver. It was not clear if there were any other casualties, said Bhusal.

In Kaski district, 150km (93 miles) west of the capital, 10 people were killed when landslides washed away three houses, Karki said.

In a social media post on Friday, Prime Minister Pushpa Kamal Dahal expressed sadness over the disasters and instructed government agencies to conduct effective search and rescue operations.

The monsoon season that begins in June and ends in September brings heavy rainfall to Nepal, often triggering landslides in the country that is mostly covered by mountains.