Residents wade through the floods
Indian Prime Minister Manmohan Singh says floods in the northern state of Bihar are a "national calamity".
He has visited areas where 55 people have died and some two million are displaced after the Kosi river breached its banks, changing course.
The prime minister has announced an aid package worth $230m.
But aid agencies say many of the victims are being moved to temporary shelters which lack basic amenities and are at risk from disease.
Accompanied by the president of the governing Congress Party Sonia Gandhi, the prime minister flew over the flood-affected area by helicopter to get a first-hand view of the devastation.
At least two million people have had to move out of their homes after the government ordered them to evacuate because of the rising waters.
Meanwhile, soldiers and air force helicopters continued to provide aid to the flood-ravaged parts.
Food and medicines were being air-dropped to the stranded people.
Hundreds of relief camps have been set up to house people evacuated from the flooded areas.
Despite the army being pressed into the relief and rescue efforts, many of the victims complained that they had received no assistance.
The floods have washed away roads and railway tracks, and water and electricity supplies have been affected in many areas.
A report released by Unicef says there are fears of infectious diseases as hundreds of thousands of homeless crowd into relief camps.