Around 130 people have died in flash floods in India's north-eastern state of Assam since Saturday.
The floods struck when many people were sleeping
The worst affected area is the district of Goalpara where at least 80 villagers are still missing, officials say.
Water came sweeping down the hills from the neighbouring state of Meghalaya on Saturday after a week of heavy rains, catching many villagers by surprise.
Officials say that areas of Goalpara remain under 2m of water, even though it is receding in some places.
Anger and frustration
Goalpara's senior relief official, AK Majumder, told the BBC that 55 relief camps have been opened for more than 25,000 people who were made homeless by the sudden floods.
Correspondents visiting the area say that many unidentified human bodies are lying in the receding water, alongside the carcasses of cattle.
Some 100,000 people in Assam are now homeless
The Indian military have been called in to assist the relief effort, with helicopters dropping essential supplies to people who have been marooned.
But the BBC's Subir Bhaumik in Calcutta says that many people are furious that they were not warned about the impending floods, and are frustrated that they received no help when the water arrived.
More than 120 villages have been fully submerged, as the wall of water swept everything on its way on Saturday.
"Villagers were caught unaware in their sleep. So many were washed away before they could react to the sudden flow of water," local resident Biju Boro was quoted as saying by Reuters news agency.
Authorities have opened about 50 relief camps to provide shelter for more than 100,000 people left homeless by the floods, officials say.
Indian air force helicopters are flying sorties round the clock to rescue the flood-marooned villagers and drop essential supplies for them.
But thousands of villagers who have escaped the floods are still without food and water after nearly 48 hours, correspondents who have visited the affected area say.
This year's rains and floods have already killed more than 2,000 people and left millions homeless in India, Bangladesh, Nepal and Pakistan.
Most of the casualties occurred during the monsoon season, which usually lasts from June to September.