Western parts of Naogaon have been submerged after the main embankment on the Atrai River collapsed due to strong currents.
The Water Development Board said that the dam collapsed on Monday morning when villagers, along with WDB workers, were trying to repair a crack in Manda.
At least 25,000 villagers of 50 villages are at risk of being stranded due to the fresh flooding.
The river was flowing 120cm above the danger level on Sunday. By the time the dam collapsed, the water level had risen to 200cm, said WDB Engineer Anwar Hossain.