More than 418,000 people have been affected in five districts of the country due to the flash floods, according to a recent report by the Needs Assessment Working Group (NAWG) in Bangladesh.
The worst affected are those living in the low-lying areas of Sylhet and Sunamganj districts, it said.
The flood situation has created an acute crisis of pure water, sanitation, food, shelter, and healthcare among the affected population, while also damaging the livelihoods of many.
Several areas have been left without power for days over the past weeks, and roads and communications have been disrupted due to floodwater.
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Though floodwater has started to recede in many areas, new challenges have emerged with the risk of a waterborne disease outbreak among the affected population in the aftermath of the floods.
Bangladesh Red Crescent Society Secretary General Kazi Shofiqul Azam said: "Severe flash flooding is battering the lives of millions in Sylhet and Sunamganj; people are in dire need of humanitarian assistance."
Red Crescent teams are carrying out rapid assessment alongside relief operations, he added.