A huge number of individuals are being evacuated downstream of a major dam that has been blown up in Russian-held Ukraine.

President Zelensky said 80 villages and towns were in danger of flooding after the destruction of the dam at Nova Kakhova, which he blamed on Russia.

Water is flooding down the Dnipro Stream and is said to represent a devastating flooding risk to the city of Kherson.

Russia has denied destroying the dam - which it controls - rather accusing Ukrainian shelling.

Neither Ukraine nor Russia's case has been checked by the BBC.

The Kakhovka dam is crucial in the region. It contains a reservoir, which provides water to farmers and residents, as well as to the Zaporizhzhia nuclear power plant. It is also a vital channel carrying water south to Russian-occupied Crimea.

Video footage shows a torrent of floodwater spouting through a breach in the dam. A few towns are as of now overflowed, while individuals in regions further downstream are currently escaping by bus and train.

Nearly 16,000 individuals are in a "critical zone", according to the head of the Kherson region, Oleksandr Prokudin.
Mr. Prokudin said water levels in the Dnipro River will be "critical" within five hours and accused Russia of committing "yet another act of terror".

In a Telegram post, he said the evacuation of residents living in the threatened areas on the Ukraine-controlled western bank of the Dnipro River was underway, and he appealed to residents on the opposite bank - currently under Russian control - to immediately leave their homes.

Mr. Prokudin said residents were being taken by bus to Kherson, from where they will be moved to different cities across the country.

People in low-lying parts of the city of Kherson - around 50 miles downstream - have also been told to evacuate as quickly as possible.

One local resident Andrei, who lives close to the dam, said he believed Russia wanted to "drown" his city.

In Kherson, Lyudmyla - who was loading her belongings including a washing machine onto a trailer that was attached to an old car - said: "We're afraid of flooding. We're taking our things a little higher up."

She called for Russian forces to be "kicked out of here... they're shooting at us. They're flooding us or doing something else".

Another resident of the city, Sergiy, said he feared "everything is going to die here". "All the living creatures and people will be flooded out," he said, gesturing at nearby houses and gardens.

There are concerns about the impact on the Zaporizhzhia nuclear power plant, which uses water from a reservoir behind the dam for cooling.

The situation there is said to be under control and the International Atomic Energy Agency (IAEA) has said it is monitoring the situation closely.

The UN agency said it saw "no immediate nuclear safety risk" at Europe's biggest atomic plant.

As well as the more immediate evacuation concerns, there are also longer-term fears about the damage.

The dam holds back the waters of the Dnipro, forming a vast reservoir that provides water for a host of communities upstream.

It is also a vital part of the channel carrying water from the Dnipro to Russian-annexed Crimea.

After Russia annexed Crimea in 2014, Ukraine blocked a channel carrying water from Nova Kakhovka, triggering a water crisis on the peninsula.

Russian forces reopened the channel soon after last year's full-scale invasion. But without the dam, dropping water levels could once again jeopardize the flow of water.

It is not yet clear what caused the breach in the dam, but Ukraine's military intelligence has accused Russia of deliberately blowing it up early this morning.

This seems plausible, as Moscow may have feared that Ukrainian forces would use the road over the dam to advance into Russian-held territory, as part of their counter-offensive.

For Russia, anxious to defend conquered territory in southern Ukraine, the dam represented an obvious problem.

Just as Ukrainian forces attacked road and rail bridges further downstream last autumn in a successful effort to isolate Russian forces in and around Kherson, Russia may have decided to destroy the dam to hold up Ukraine's counter-offensive, which it fears could come from multiple directions.

However, a Russian official claims Ukraine carried out the attack on the dam to detract from what they said were the failures of its counter-offensive and to deprive Crimea of fresh water.

The Russian-installed mayor of Nova Kakhovka said Ukraine had carried out a "terrorist act directed against civilians", adding that that the "city is flooded".

The Kremlin also claimed Ukraine carried out the attack as an "act of sabotage", to detract from what they said were the failures of its counter-offensive and to deprive Crimea of fresh water.

A major Ukrainian push has long been expected. Kyiv has already said it would not give advance warning of its start but a recent increase in military activity is being seen as a fresh sign that the counter-offensive may have begun.

Senior Ukrainian military commander Serhiy Naev said the dam blast would not stop Ukraine from advancing.

On Monday, Ukraine's deputy defense minister said around the "epicenter of hostilities" in Bakhmut, but did not say whether the counter-offensive had begun.

Bakhmut has for months been at the heart of fierce fighting. It has little strategic value - but is important symbolically both for Kyiv and Moscow.

In the aftermath of the attack on the dam, Mr. Zelensky said he had called a meeting of the country's security and defense council.

Blaming "Russian terrorists" for the partial destruction of the dam, Mr. Zelenksy said, "It's only Ukraine's victory that will return security".

Yuri Sak, an adviser to Ukraine's Ministry of Defense, told BBC Radio 4's Today program that phone intercepts have suggested Russia wants to target more dams.

"They're actually calling to blow up more dams on the Dnipro River," he said.

Ukraine has branded the attack on the dam "ecocide" and said that 150 tonnes of engine oil has spilled into the Dnipro River.

World leaders have laid the blame for the blast at Russia's door, with some calling it a war crime.

UK Foreign Secretary James Cleverly branded the attack an "abhorrent act", adding: "Intentionally attacking exclusively civilian infrastructure is a war crime. The UK stands ready to support Ukraine and those affected by this catastrophe."

The head of Nato, Jens Stoltenberg, said the destruction of the dam demonstrated once again the brutality of Russia's war in Ukraine, while Charles Michel, the president of the European Council, said he was "shocked by the unprecedented attack"

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