A furious row has broken out between aid agencies and Indian authorities over allegations that flood-hit areas had inadequate food supplies and medical equipment to cope with the annual monsoon deluge.
More than 250,000 refugees are in government and relief agency camps in Bihar state, northern India, and many aid workers say that tensions are growing over the lack of emergency supplies.
Television pictures showed people fighting to get places in boats as soldiers in lifejackets attempted to restore order.
In a statement, ActionAid said "lessons from the past disasters should be kept in mind while planning response … a long-term comprehensive response is necessary to deal with relief, recovery and disaster preparedness".
However government officials said the Bihar floods were an unprecedented event. The Kosi river, which flows from Nepal, burst its banks two weeks ago, changing course and flooding surrounding areas.
"This has never happened before. How can you suggest that we could plan for this? Tell me which state can cope with hundreds of thousands of people losing everything," Prataya Amrit, a disaster management official in Bihar, told reporters.
Relief workers said many people were refusing to leave their submerged homes.
"They don't want to leave their assets, even in this desperate situation," Vinay Ohdar, the head of operations for ActionAid in Bihar, said. "We are getting reports of people staying with cattle and with rice stocks. They are afraid of looting."
For those in camps, matters are expected to get worse before they get better. The government said it expected 1 million flood refugees, with fears that crowded and often unsanitary conditions could lead to outbreaks of diseases such as cholera.
The UN warned that "the heat, combined with limited supplies of safe drinking water and poor hygiene conditions, poses a great risk of water and vector-borne diseases".
The Flood Forecasting Centre said the flood situation could worsen in the next couple of days as the country's three major rivers continued to rise alarmingly. Flood alerts have been issued in southern India.