In Assam, the mighty Brahmaputra River burst its banks at several places Saturday washing away homes and breaching roads and mud embankments.
"A total of 19 of the state's 24 districts were hit by the floods affecting some 916,453 people," an Assam government statement said Sunday.
At least 10,000 people have been displaced in the neighbouring state of Tripura.
The second wave of floods that began on June 27 in Assam has claimed the lives of 13 people in the region so far.
About 400,000 people were displaced during the first wave of floods in early June, but the waters later receded.
"The situation has turned critical in many parts of the state with the river taking a deadly mood," Assam Revenue Minister Mithias Tudu told AFP.
An outbreak of malaria and waterborne diseases in flood-hit areas is adding to the woes of the people.
At least nine more people died of malaria in various parts of eastern and western Assam during the past week, taking the toll due to malaria and Japanese encephalitis to 69 since the beginning of June.
"We have adequate stocks of anti-malarial drugs, but we don't have enough manpower to deal with the situation," said P.C. Bhattacharya, Joint Director of the Assam Health Department.
For tens of thousands of people taking shelter on mud embankments and other raised platforms, there has been acute shortages of food and drinking water.
"So far we are yet to get any government relief in the form of rations or other supplies," Tarini Deka, a village elder in the eastern district of Morigaon, told AFP.
"We are starving and if the government does not come to our aid soon, many people will die of hunger."
The Brahmaputra was still flowing above the danger level at various places although the trend was receding, a Central Water Commission bulletin said Sunday.
In the eastern state of Bihar, some 200,000 have been affected by floods, officials said, but could not say how many of those had beee made homeless.
All major rivers in the state, especially in the northern districts, were flowing above danger levels as waters spilled into residential areas at several places, they said.
The local media have put the death toll from the floods at 12 but the relief department has not confirmed any so far.
More than 350 people were killed in the state in floods last year.