Kherson, Ukraine - A Russian-held dam in southern Ukraine was damaged on Tuesday, with Kyiv and Moscow accusing each other of blowing it up while locals were forced to flee rising waters.

The Kakhovka dam was partially destroyed by "multiple strikes", Moscow-installed authorities claimed just as expectations were rising over the start of Ukraine's long-awaited offensive.

Ukraine, however, accused Russia of blowing up the hydroelectric plant.

"The terrorists' goal is obvious – to create obstacles for the offensive actions of the armed forces," Ukrainian presidential aide Mykhaylo Podolyak said.

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Ukrainian President Volodymyr Zelensky convened a meeting of his National Security Council over the Russian "war crime", said his chief of staff, Andriy Yermak.

Several villages have been "completely or partially flooded" following damage to the dam and evacuations from the area have begun, a Ukrainian official said.

"About 16,000 people are in the critical zone on the right bank of the Kherson region," Oleksandr Prokudin, head of the Kherson military administration, said on social media, adding that there was flooding in eight areas along the Dnipro River.

The Kakhovka dam, seized at the start of the Russian offensive in Ukraine, notably supplies water necessary to cool the Zaporizhzhia nuclear plant, which has already come perilously close to being damaged by shelling.

Energoatom, the Ukrainian nuclear operator, said the incident was "an additional threat" to the power plant, but the UN and Russia insisted there was no major risk at the moment.

Built on the Dnipro River in 1956, during the Soviet era, the structure is partly made of concrete and partly of earth

It is one of the largest pieces of infrastructure of its kind in Ukraine.