Floodwaters are continuing to rise in South Asia, where more than 20 million people have been left stranded and hungry in scores of ravaged villages.
Many villages are under water in Assam, as residents seek help
Officials say more than 11 million people are suffering acutely in India's poorest state, Bihar.
More than 100 people have died in the floods in Bangladesh and India.
The United Nations Children's Fund (Unicef) says urgent action is needed to prevent epidemics of dysentery and cholera in the affected areas.
The BBC's Anu Anand in Delhi says many of the survivors in Bihar are still clinging to rooftops, and have been without much food for nearly a week.
She says the Indian army is continuing to distribute aid, but so far there has not been a large-scale relief effort, and water-borne diseases remain a threat.
In the Indian state of Assam the chief minister says there is an urgent need for more relief supplies.
"The flood situation still remains very critical, with nearly nine million people uprooted from their homes," Chief Minister Tarun Gogoi told the AFP news agency.
Air force helicopters have been dropping relief and food to the affected people in both Bihar and Assam.
But officials say medical supplies need to be increased to ward off the threat of disease.
"The post-flood situation is always very dangerous, when we generally find outbreaks of water-borne diseases among the victims," Assam Health Minister Bhumidhar Barman said.
Threat to Dhaka area
Flood warning officials in Bangladesh say waters rolling down from the north of the country have aggravated problems in central areas.
They are warning that more areas around the capital, Dhaka, could be flooded at the weekend.
Thirty-three of Bangladesh's 64 districts have been affected, leaving at least three million people homeless or marooned.
The situation in north and north-eastern districts has improved.
Unicef says the first consignment of one million water purification tablets should be delivered to Bangladesh on Saturday.
"We want to avoid epidemics which in such cases can spread very rapidly especially with temperatures now above 35 degrees Celsius," Unicef spokesman Damien Personnaz said.
Floods and landslides are common in South Asia during the monsoon season, when annual rains combine with melting snow from the Himalayas.
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