Rescue workers pressed ahead on Wednesday to evacuate people across an expansive area of southern Ukraine flooded by the destruction of the Kakhovka dam a day earlier, as another humanitarian disaster unfolded along the front lines of the war.

Floodwaters, which were expected to peak on Wednesday morning, engulfed streets and homes in dozens of communities, sent residents fleeing on boats, and dislodged roofs that floated away. According to Ukrainian officials, an estimated 16,000 people were at risk on the Ukrainian-controlled western bank of the Dnipro river, and 25,000 more would need to be evacuated on the eastern bank, which is under Russian control.

As the scale of the disaster began to come into focus, President Volodymyr Zelensky of Ukraine said that hundreds of thousands of people were “without normal access to drinking water” and that the emergency services were working to provide assistance in Ukrainian-controlled areas.

The Russian-installed administrators of Nova Kakhovka, the city adjacent to the dam and attached hydroelectric plant, said floodwaters had begun receding on Wednesday morning. Seven people were reported missing, they said, while cautioning that those were preliminary figures.

Experts said a deliberate explosion inside the dam, which has been under Russian control since early in the war, most likely caused the massive structure of steel-reinforced concrete to crumble.

Moscow blamed Ukraine, calling the blast an act of sabotage, but did not elaborate on how it might have been done. Zelensky said Russian forces had blown up the dam to “use the flood as a weapon”.

But he said that the destruction of the dam would “not affect Ukraine’s ability to de-occupy its own territories”, an apparent reference to a counteroffensive by Ukrainian forces that American and Russian officials said this week might have begun east of the Dnipro.

Up to 100 people in Nova Kakhovka were trapped and thousands of wild animals were killed after the Kakhovka dam collapsed, the town’s Russian-installed mayor said, Russian news agencies reported.

Over 30,000 cubic metres of water was pouring out of the reservoir the dam held back every second and the town was at risk of contamination from the floods, the Tass news agency quoted the official, Vladimir Leontyev, as saying.

He said rescue efforts were being undertaken to free people trapped by the floods.

New York Times News Service and Reuters