Landslides and floods triggered by heavy downpours in Nepal and neighbouring India have killed more than 60 people, officials said on Sunday, as rescue workers raced to reach cut-off communities in remote mountainous terrain.

Torrential downpours have lashed Nepal since Friday, leaving rivers in spate and many areas in the Himalayan nation inundated.

At least 43 people have died in rain-triggered disasters and five are missing, Nepal's National Disaster Risk Reduction and Management Authority said.

At least 37 were killed by landslides in the worst-affected eastern district of Illam.

Rivers in the capital Kathmandu have also swelled, inundating settlements along their banks.

Security personnel were deployed to assist rescue efforts with helicopters and motorboats.

Landslides have blocked several highways and disrupted flights, leaving hundreds of travellers – many returning after celebrating the Hindu festival of Dashain – stranded.

Prime Minister Sushila Karki said government agencies were "fully prepared for rescue and relief".

"Your safety is our utmost concern. Do not hesitate to seek necessary assistance," she said in an address, adding that the government has declared Sunday and Monday public holidays and urged people not to travel unless necessary.

Across the border in India, at least 20 people were killed in the tea-growing hill district of Darjeeling in West Bengal state after heavy overnight rain unleashed flash floods and landslides that destroyed homes and infrastructure.

Footage on Indian television news showed rescue workers using cables to access cut-off regions as raging waters smashed into bridges and caved in roads. (AFP)