Heavy monsoon rains have caused fresh floods in new areas of India with dozens of villages affected in the western state of Gujarat.
In north India, where water is receding after two weeks of floods, health workers are starting a clear up.
The UN has blamed the flooding on climate change and says such disasters are becoming increasingly common.
About 28m people have been affected by the floods in India, Bangladesh and Nepal. More than 400 people have died.
Struggling
Indian air force helicopters joined army and civil authorities in rescue operations after torrential rains cut off more than 400 villages in Gujarat, killing at least seven people, news agency Associated Press quoted DA Satya, a top state official, as saying.
The worst-hit Junagadh district received 471mm (18.5in) of rain in 24 hours, submerging several villages under six feet (1.83m) of water, Mr Satya said.
More than 17,000 people have been shifted to camps on higher ground in Rajkot, Junagadh, Jamnagar, Surat and Porbander districts where 564 villages are left without electricity, he said.
Meanwhile, food, drinking water and medicines are being distributed across north India but the scale of the disaster has dwarfed relief efforts.
Aid workers are still struggling to get to many of the affected.
Meanwhile, a senior UN official said the severe flooding in parts of South Asia was the result of climate change and that such disasters were becoming increasingly common.
Under Secretary General for Humanitarian Affairs, John Holmes, who is in Sri Lanka, said: "It is perfectly clear to us that natural disasters of this kind, extreme weather events, are more frequent and more intense."
He said more must be done to ensure people living in vulnerable areas would be able to cope.
Contamination
The UN has warned of a health crisis in the South Asian regions affected unless relief work is stepped up.
THE ASIAN MONSOON
"Entire villages are days away from a health crisis if people are not reached," Unicef's health chief in India, Marzio Babille, has said.
India is the worst-affected country, with some 20 million people in the states of Assam, Bihar and Uttar Pradesh hit by the floods, according to the UN.
Some eight million people are affected in Bangladesh and another 300,000 people in southern Nepal.
Although water levels are receding in Nepal and Bangladesh, millions of people are still marooned on high ground.
The international aid agency Oxfam has launched a $2m appeal to help about 200,000 people across South Asia with essential food, clean water and shelter.
Most water sources in affected areas are said to be either contaminated or submerged.
The World Health Organisation and Unicef said stagnant water was "a lethal breeding ground" for diseases.
About 1,400 cases of diarrhoea have been reported in Bangladesh this week, the Word Health Organisation said.
One Bangladeshi on the outskirts of Dhaka, Mohammed Amin, told Reuters news agency: "My children wait for me to bring them something to eat, but I am so helpless."
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