Heavy rains for the last few days, and water from upstream, further flooded low-lying areas in Rangamati, Khagrachhari, Sylhet, Sunamganj and Nilphamari districts.
Various parts of Barkol and Bilaichhari upazilas in Rangamati went under water following torrential rains and the onrush of water from the hills.
Kaptai Lake was also above the danger level on Wednesday.
Sources at Kaptai Water and Electricity Centre said the authorities concerned have opened eight out of 16 gates of the spillway of the dam to release 4,500 cusecs of water to the Karnaphuli River to avoid the danger and to handle the excessive pressure of water.
Meanwhile, road communications between Chattogram and Rangamati remained suspended since Tuesday morning due to landslides at different points on the road.
However, communications on internal routes in Rangamati remained normal.
In Khagrachhari, different parts of Dighinala upazila, which had experienced serious flooding barely two weeks ago, were flooded again on Wednesday due to torrential rains for the last two days.
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Locals said the Dighinala-Langdu road went under water, disrupting communication.
Farmers fear a huge loss of crops due to the floods.
In Sunamganj, several hundred thousand people were marooned in Dowarabazar, Shalla, Tahirpur, and Dharamapasha upazilas due to floods caused by the rains.
The Surma River was flowing 80cm above the danger level at Sholosahar point.
Also, low-lying areas -- Sahebbari, Nabinagar and Natunbazar -- of the town went under water and many educational institutions were closed, swamped by rainwater.
The local Water Development Board recorded 120mm of rainfall till Wednesday morning.
District Relief and Rehabilitation officer Faridul Haque said that every upazila has been allocated 10 tonnes of rice and Tk50,000.
In Sylhet, over 1,00,000 people are marooned by the floods caused by heavy rains inundating low-lying areas in Goainghat upazila of the district. The Piyain and Sari rivers are flowing 46 centimeters above the danger level.
In Nilphamari, a number of villages in Dimla and Jaldhaka upazilas were flooded by the rising waters of the Teesta River, said local public representatives.
The Teesta was flowing 5cm below the danger level at Teesta Barrage point, said Dimla Water Development Board official, Nurul Islam, adding that 44 sluice gates of the Teesta Barrage were kept open.
Heavy to very heavy rainfall with gusty winds are likely at places in Rangpur, Mymensingh, Sylhet and Chattogram divisions, due to active monsoon weather during the next 24 hours, commencing 6pm on Wednesday.