Pictures from Bangladesh show houses standing in water and people wading through the streets with water up to their knees.
In the floods, which are described as the worst in nearly 20 years, large dikes along the Barak River have broken and over 100 villages in the Zakiganj district in the northeast are under water.
New torrential rains are expected in India, which will fill the rivers and cause further flooding in the area.
At the same time, the authorities warn that the dikes can only be repaired once the water has receded.