The numbers of fatal floods and landslides caused by monsoon rains have increased in recent years.
At least 14 people have been killed after heavy rains triggered flash floods and landslides across Nepal, with disaster teams searching for nine missing, police said on Sunday.
Flooding in neighbouring India and Bangladesh has also caused widespread damage and affected millions.
“Police are working with other agencies and locals to find the missing people,” said Nepalese police spokesman Dan Bahadur Karki.
People have been killed or are missing in multiple locations, he said.
Monsoon rains from June to September bring widespread death and destruction every year across South Asia, but the numbers of fatal floods and landslides have increased in recent years.
Experts say climate change and increased road construction are exacerbating the problem.
Parts of Nepal have been receiving heavy rainfall since Thursday, prompting disaster management authorities in the Himalayan nation to warn of flash floods in multiple rivers.
There have been reports of floods in several districts of lowland areas bordering India.
Last month, 14 people were killed in Nepal in ferocious storms that brought landslides, lightning and flooding.
In India, floods have swamped the northeastern state of Assam, with six people killed in the last 24 hours, the Assam State Disaster Management Authority said on Sunday.
That takes the death toll from downpours in the state since mid-May to 70, according to the PTI news agency.
In low-lying Bangladesh, downstream from India, the disaster management agency said floods had hit more than two million people.
Much of the country is made up of deltas where the Himalayan rivers the Ganges and the Brahmaputra wind towards the sea after coursing through India.
The summer monsoon brings South Asia 70-80 percent of its annual rainfall.
