The situation turned grim on Thursday after the surging waters of the Brahmaputra, one of Asia's largest rivers, breached a 100-metre stretch of a newly built embankment in Lakhimpur district in Assam state.
At least 300 villages in the district, about 350 kilometres north of the state capital Gauhati, have been flooded after the breach, Assam Revenue Minister Bhumidhar Barman said.
While some people have left for higher ground, the majority are still in their homes, even though flood waters have entered most houses.
'We have sounded a maximum alert and have deployed paramilitary disaster response teams for rescue operations,' said Ataul Karim, the district police chief.
Monsoon floods are routine in Assam, a state of 26 million people, with heavy rains swelling the Brahmaputra and its innumerable tributaries that crisscross the state. Last year, millions of people were forced to temporarily abandon their homes.
The monsoon rains usually hit India from June to September.
The rains are crucial for farmers whose crops feed hundreds of millions of people, but they also bring massive destruction across the country. Every year, thousands of people are killed by flooding, collapsing houses and other rain-related incidents.