Flash floods and landslides have killed at least 68 people in Nepal in the past three days and another 15 are missing, local authorities say.
Rescue teams of soldiers and police personnel used rubber boats and helicopters to rescue people from rooftops and trees, Yadav Koirala, spokesman for Nepal's home ministry, said on Thursday.
Some waded through waist-deep water with women and children, police said.
In the western town of Butwal, 170km from Kathmandu, local TV stations showed the Tinau river washing away a huge suspension bridge.
Dramatic footage shot from a smartphone by Yub Raj Rana, a local, also showed the Tinau breaching a concrete embankment, forcing him to flee a tide of water until he reached the safety of higher ground.
In neighbouring India, nearly 1.7 million people have been affected by floods and 15 lives lost as the situation remained critical the northeast state of Assam with rivers continuing to overflow, local authorities said.
There was some respite from incessant rains on Thursday.
Floods and landslides are common in India and Nepal during the June-September monsoon season and the death toll runs into the hundreds every year.
The oil-rich and tea-growing state of Assam is under water except for a few districts, the state forest minister said.
The Brahmaputra, Assam's main river which is fed by Himalayan snow melt and monsoon rains, has burst its banks in many areas along its course.
The majority of Assam's land area is in the Brahmaputra valley.
"The situation is still very bad. We are taking measures to help people in every possible way," Indian Forest Minister Pramila Rani Brahma said.
The army has been deployed to repair dams washed away by gushing waters and helicopters have been pressed into action to distribute food and medicines to homeless people who have taken shelter on highways and in hilly areas.
Local officials have opened around 500 temporary shelters and more than 150 distribution camps for the displaced people, officials at the state disaster management authority said.