Thousands of people have been evacuated after an attack on a major dam unleashed a torrent of water, inundating two dozen villages and sparking fears of "grave and far-reaching consequences".

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Moscow and Kyiv have traded blame for ripping a gaping hole in the Kakhovka dam, which is located on the front line and provides cooling water for Europe's largest nuclear plant.

A state of emergency has been imposed in Kherson, Russia's TASS state news agency reported on Wednesday.

The agency, citing emergency services, said about 2,700 houses were flooded after the destruction of the dam on Tuesday and almost 1,300 people had been evacuated. At least seven people were missing, officials said.

The destruction of the dam on the Dnipro River flooded a large part of the front line in the Kherson region.

Residents sloshed through knee-deep waters in inundated homes as videos posted on social media showed scenes, including rescue workers carrying people to safety, and what looked like the triangular roof of an entire building that had been uprooted drifting downstream. Footage taken from the air showed waters filling the streets on the eastern side of the river.

In a statement on Tuesday, the Russian Foreign Ministry strongly condemned the destruction of the power plant "by the armed forces of Ukraine", calling on the international community "to condemn the criminal acts of the Ukrainian authorities".

Earlier in the day, Ukrainian President Volodymyr Zelensky said Russian forces had destroyed the dam. According to Ukraine's state-run nuclear energy operator Energoatom, the destruction of the dam may have negative consequences for the Zaporizhzhia plant.

UN Secretary-General Antonio Guterres called the attack "another devastating consequence" of the conflict between Russia and Ukraine.

UN Undersecretary-General for Humanitarian Affairs and Emergency Relief Coordinator Martin Griffiths on Tuesday warned of the grave consequences of the destruction of the dam, describing it as possibly the most significant incident of damage to civilian infrastructure since the start of the Russia-Ukraine conflict in February 2022.

"The sheer magnitude of the catastrophe will only become fully realized in the coming days. But it is already clear that it will have grave and far-reaching consequences for thousands of people in southern Ukraine," he told an emergency meeting of the UN Security Council.

A Chinese envoy on Tuesday also voiced grave concerns over the destruction of the dam.

The protection of civilians and critical civilian facilities in armed conflict is an important principle enshrined in international humanitarian law, said Zhang Jun, China's permanent representative to the UN.

"We are deeply concerned about the resulting humanitarian, economic, and ecological consequences. We call on all parties to the conflict to abide by international humanitarian law and do their utmost to protect civilians and civilian infrastructure," he said.

The reservoir, formed by the dam, is also a major source of cooling water for the Zaporizhzhia nuclear power plant. China notes that the director-general of the International Atomic Energy Agency has confirmed that the dam's destruction has not posed any safety risk to the nuclear power plant. However, as the water in the reservoir continues to recede, it may not be possible to continue pumping water to the nuclear power plant in the future.

The director of the plant, Yuri Chernichuk, said water levels in the cooling pond had not changed and "at the moment, there is no security threat to the Zaporizhzhia nuclear power plant".

In another development, Russia's defense ministry said on Wednesday that "Ukrainian saboteurs" had blown up a section of the Togliatti-Odesa ammonia pipeline that carries fertilizer from Russia to Ukraine in Kharkiv region on Tuesday.

There was no immediate comment from Ukraine.

Agencies via Xinhua