KHERSON, Ukraine (AP) — Floodwaters from a collapsed dam kept rising in southern Ukraine on Wednesday, forcing hundreds of people to flee their homes in a major emergency operation that brought a dramatic new dimension to the war with Russia, now in its 16th month.

Amid the disaster response, artillery shelling rang out as people scrambled to get out of the danger zone, climbing onto military trucks or rafts.

A day after the dam’s collapse, it remained unclear what caused it. Ukraine accused Russia of blowing up the dam wall, while Russia blamed Ukrainian shelling for the breach. Some experts said the collapse may have been an accident caused by wartime damage and neglect, although others said this was unlikely and argued that Russia might have had tactical military reasons to destroy the dam.

The flood’s force was expected to slacken as the day wore on, officials said Wednesday, but water levels were expected to rise by another metre (about three feet) over the following 20 hours and engulf more downriver areas along the banks of the Dnieper.

The Kakhovka hydroelectric dam and reservoir, one of the largest in the world and essential for the supply of drinking water and irrigation to a huge area of southern Ukraine, lies in a part of the Kherson region occupied by the Kremlin’s forces for the past year. The Dnieper River separates the warring sides there.

Ukraine President Volodymyr Zelenskyy on Wednesday accused Moscow of “deliberate destruction” of the dam.

“Hundreds of thousands of people were left without normal access to drinking water,” he said in a Telegram post.

Some local residents spent the night on rooftops. Others, scrambling to flee the rising waters, were evacuated by buses and trains with the belongings they could carry.

“The intensity of floods is slightly decreasing,” Oleksandr Prokudin, the head of Kherson Regional Military administration, said in a video. “However, due to the significant destruction of the dam, the water will keep coming.”