Rescuers in rubber boats struggled to reach villagers marooned by the swollen Bhahmaputra river that is fed by snow from the Himalayas and flows through Assam before entering Bangladesh and emptying into the Bay of Bengal.

Three people drowned and 25,000 people moved to safer areas overnight as floodwaters swamped fresh parts of eastern and northern Assam, officials said.

"Two weeks of flooding have left 15 people dead and more than 1.9 million displaced so far, most of them taking shelter in makeshift relief camps," a Flood Control Department official said.

Forecasters predicted more rain across the state over the next two days.

"The Brahmaputra and its tributaries are flowing above the danger level in many parts of the state with the water current in some areas abnormally high," a government statement said.

Flooding caused by India's monsoon, which lasts from June to September, leaves a trail of destruction in the oil- and tea-rich state and the rest of the country every year.

It washes away villages, submerges crops and drowns livestock and people.

"A total of about 400 villages have come under water with the worst-hit being Dhemaji district in eastern Assam," Assam Chief Minister Tarun Gogoi told AFP.

Roads to remote areas in eastern Assam were cut by the floodwaters.

Medical teams carrying medicines and water purifying tablets were fanning out to hardest-hit districts to avert water-borne diseases, Assam Health Minister Bhumidhar Barman said.

Last year at least 200 people died and more than 12 million were displaced by floods that hit Assam.

Torrential rain lashed the western coastal state of Gujarat early this month, killing at least 132 people in flooding and mudslides. The waters there have now receded.