On Sunday 30 bodies were recovered from paddy fields and deserted houses in Assam's Goalpara district, the area worst affected by the floods, said a rescue official who did not wish to be named.
The bodies of seven others who had drowned in different incidents in adjoining Meghalaya state were recovered by the army, a government official said.
Thousands of people were still taking shelter on high-rise embankments and the edges of highways in Assam, witnesses said.
Weather officials said the deluge was caused by a depression in the Bay of Bengal, but the skies were expected to clear soon.
Authorities fear the toll could rise with reports of many more people missing from remote areas.
Scenes of death and devastation were everywhere in Goalpara's Bolbola village, 130km west of Assam's main city of Guwahati.
Floods in north-eastern India
have left 100,000 displaced
Vultures, crows and other birds of prey circled above drawn by the stench of decaying animal carcasses.
Indian soldiers piled bodies up in Bolbola village, as they called in rescue workers.
"We were sleeping when flood waters surrounded us in a flash and before I could react I saw my son swept away," said a distraught Hamid Islam, a farmer from Bolbola.
The body of Islam's six-year-old son was one of those recovered on Sunday.
"Never in my life have I seen such a devastating flood," said Binoy Das, a long-time resident of Bolbola.
Vehicles overturned or swept from the road by strong currents lay submerged in water, witnesses said.
Army helicopters rescued scores of people in the area, many of whom had climbed trees to escape the flash floods.
In other areas, rescue workers used rubber rafts and boats to reach pockets of isolated and marooned people who had taken refuge on rooftops and any available piece of elevated land.
Officials said nearly 100,000 people had been displaced in the state.
Heavy rains have also lashed the eastern Indian state of West Bengal, where 14 people have lost their lives since Thursday.
In neighbouring Bangladesh, at least 11 people were killed and hundreds more injured by a series of tornadoes that ripped through towns and villages on Thursday, officials said.