In the last two weeks, the Indian Army and Air Force have had to evacuate thousands of people. Helicopters are unloading essential items for people stranded at risky places in the worst-hit Dima Hasao district. The Indian Space Research Organization is using satellites to determine the damage.
Extreme levels of flood danger were announced in Sylhet and Sunamganj districts of Bangladesh, bordering northeastern India.
Arifuzzaman Bhuiyan, executive engineer of the Flood Forecasting and Warning Center in Dhaka, the capital of the country, said water from at least three rivers was flowing over the danger line on Monday.
Bangladeshi media say hundreds of villages have been inundated and crop fields have been severely damaged. There is also a shortage of drinking water for the people as the wells are under flood water or the water supply system is damaged.
No casualties have been reported in Bangladesh so far.
According to the Jamuna TV station, although the flood waters started receding from some areas, many areas were affected by the new floods on Monday.
Authorities said hundreds of villages were cut off from electricity and roads were badly damaged.