Floodwaters rushing down from highlands in India have inundated much of the low lying areas of Sylhet and Sunamganj districts.
While the Surma river has swollen above the danger level, water levels of the Cholti, Patli and Jadukata rivers are rising every day.
Heavy rain upstream, in India's Meghalaya, is aggravating the situation.
At least 182 flooded schools and colleges in the districts have been forced to close.
Part of Sylhet's Gowainghat upazila is flooded while Kanaighat and Fenchuganj are likely to be inundated soon.
People in Sunamganj town, Tahirpur, Chhatak and Bishwamvarpur upazilas are also suffering in the flood.
According to the Flood Forecasting and Warning Centre of Water Development Board, the Surma and other rivers in the region have been overflowing for the last couple of days due to excessive rainfall.
Surma was flowing 102cm above the danger level on Wednesday night in Kanaighat upazila, 33cm above in Sylhet city and 70cm in Sunamganj town.
The swollen Pirayin, Gowain, Sari and other rivers are wreaking havoc in nine unions of Gowainghat, Abdul Hakim Chowdhury, Gowainghat upazila chairman, said.
In Sunamganj's Chhatak, about a hundred of villages in six unions have been flooded, Oliur Rahman, Chhatak upazila chairman, said.
Bodrul Kadir, vice-chairman of Sunamganj sadar, said many of his constituents' homes were flooded.
The road between Tahirpur and Sunamganj town has been flooded and closed to traffic, said Kamruzzaman Kamrul, Tahirpur upazila chairman.
Thousands of families are living in fear of losing their homestead, he added.
People who took shelter on the embankments of the upazila are living in the open and suffering from shortages of drinking water and food, locals said.
Ponchanon Bala, primary education officer in Sunamganj, said 33 flooded primary schools have been closed in the district. At least 100 other primary schools are affected.
Jahangir Alam, district education officer in Sunamganj, said 11 secondary schools and colleges were closed.
Anisuzzaman, agriculture officer in Gowainghat, said over 1,000 hectares of paddy fields have been flooded in the upazila.
Harunur Rashid, Bishwamvarpur upazila chairman, said thousands of people were suffering in the haor areas.
In Sunamganj town, Nabinagar, Tegharia and Jalilpur areas have been flooded due to the excessive rain.
Obaidullah, primary education officer in Sylhet, said, 88 flooded primary schools were closed, and 156 others seriously affected.
Gulzar Ahmed, education officer in Sylhet, said 50 secondary schools and colleges were also closed in the district.