The BBC's Damian Grammaticas joins one group of survivors heading to a relief camp
India has stepped up its efforts to assist half a million people displaced by severe flooding in Bihar state.
Reports say the military has poured fresh troops, doctors and medical equipment into the devastated north.
Tens of thousands of survivors have crowded into unsanitary relief camps, where tensions are growing over the desperate lack of emergency supplies.
Monsoon rains caused a river to change course cutting across Bihar, affecting areas not normally prone to floods.
At least 75 people have been killed in Bihar - but officials have warned that the death toll could climb once the situation in remote areas becomes clear.
Reports suggest that some villages have simply been washed away by strong currents.
In the north-eastern state of Assam, monsoon rains have caused the Brahmaputra river to burst its banks, displacing hundreds of thousands of people.
More than 100 villages have been completely submerged in the past 24 hours, officials said.
Across the border in Nepal, tens of thousands of people have also been displaced.
More than half a million people have been evacuated from the disaster zone, and officials hope to rescue the other 500,000 in the next few days, disaster management officials said.
The military said it was sending thousands more troops as well as helicopters and boats to Bihar, which is one of India's poorest states.
With the numbers of people in the camps expected to nearly double in the coming days, there are fears that poor conditions could lead to outbreaks of diseases such as cholera.
The United Nations 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 temporary camps are being supported by volunteers and community groups, but a lack of central co-ordination is hampering efforts.
Visiting the Bageecha relief camp in Purnea, the BBC's Sanjoy Majumder could find no camp co-ordinator or government official in charge of distributing aid.
Trucks and vans carrying aid stood parked on the highway as volunteers waited to be organised, he said.
The situation was symptomatic of what was happening across Bihar's flood-affected areas, our correspondent says.
The disaster began on 18 August when a dam burst on the Saptakoshi river in Nepal.
The Saptakoshi, which becomes the Kosi when it enters India, subsequently broke its banks in Bihar.
Officials in Nepal say hundreds of people there have been hit by illnesses such as diarrhoea and pneumonia, and an estimated 50,000 are homeless.
They say nearly 1,000 houses have been completely destroyed, and that power supplies and transport have been severely affected.
The costs to the economy are now estimated at one billion Nepalese rupees ($14.25m).
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