Russian state-owned news agency TASS reported that the decree was made by local Moscow-backed authorities around the Nova Kakhovka dam.

The Russian-installed administration of Ukraine's Kherson region said evacuations were being prepared in the Nova Kakhovka, Golo Pristan and Oleshky districts, the latter two across the mouth of the Dnipro river from the Ukrainian-held regional capital, Kherson.

Wagner chief claims Russia used 'lethal force' against mercenaries - Ukraine latest

The water level in the town of Nova Kakhovka is now up by 11 metres, according to its Russian-installed mayor, who said that the town was now underwater and that around 600 houses had been flooded.

"The water continues to mount. An evacuation is being carried out of civilians from the adjacent flooded zones to preserve all lives ... There is no panic in the town," Vladimir Leontyev said in a video message on Telegram.

An emergencies official alongside him said the water below the dam was expected to keep rising for 72 hours before subsiding and allowing a clean-up operation.

TASS said half the span of the 3.2km-long dam had been destroyed, and the collapse of the remainder was ongoing.

Ukraine's state hydroelectric agency said that the plant had been "totally destroyed" after a blast in its engine room and could not be restored.

RIA also reported, citing the Kherson region's head, that 22,000 people in 14 settlements had been affected so far.

Rescue efforts

Evacuations have started on both the Ukrainian and Russian sides of the river.

In Nova Kakhovka residents were told to "collect personal belongings and documents, take food for three days and drinking water. Turn off gas and water before leaving your residential buildings"

A zoo called Kazkova Dibrova, located on the bank of the Dnipro, was completely flooded and all 300 animals were dead, a representative said via the zoo's Facebook account.

"The park was mined and it was impossible to evacuate the animals. We tried to save them. Every day, under fire, two workers risked their lives to go to Dibrova to feed the animals," the representative said. "Now Russia has destroyed everything. Our soul is torn by pain."

On the northern side of the river, Ukraine's interior minister said Russia was shelling areas in the southern region of Kherson from where people were being evacuated on Tuesday after the destruction of the Kakhovka dam, and that two police officers had been wounded.

"The Russian military continue to shell territory where evacuation measures are being carried out. An hour ago, two police officers were wounded in the area. Shelling continues at the moment," Interior Minister Ihor Klymenko told Ukrainian television.

The Ukrainian Interior Ministry called for residents of 10 villages on the Dnipro river's right bank and parts of the city of Kherson to gather "essential documents and pets, turn off appliances and leave".

Blame game

Both Ukrainian and Russian officials blamed each other for destroying the dam. Ukraine's military said that Russian forces blew up the dam.

"The Kakhovka [dam] was blown up by the Russian occupying forces," the south command of Ukraine's armed forces said on Tuesday on Facebook.

"The scale of the destruction, the speed and volumes of water, and the likely areas of inundation are being clarified."

President Volodymyr Zelenskyy blamed "Russian terrorists" in a Telegram post, saying "the destruction of the Kakhovka hydroelectric power plant dam only confirms for the whole world that they must be expelled from every corner of Ukrainian land".

Andriy Yermak, the head of president Zelenskyy's administration, wrote on Telegram that the destruction was an attempt to "raise the stakes" in its full-scale invasion and stoke fears of a nuclear catastrophe.

"Today, the world must... understand that this is an attempt by terrorists to raise the stakes and scare everyone with a possible nuclear disaster," he wrote.

Russian forces blew up the dam "in a panic", Ukraine's military intelligence agency added.

Click to subscribe to the Sky News Daily wherever you get your podcasts

The office of Ukraine's prosecutor general has started "urgent investigations" into whether the blast is a war crime or could be possible criminal environmental destruction, or 'ecocide'. Ukraine is one of a small number of states, including Russia, that have criminalised 'ecocide'.

Kremlin spokesman Dmitry Peskov said that Ukraine had sabotaged the dam to distract attention from its faltering counteroffensive and was also intended to deprive Crimea of the fresh water it receives from the reservoir.

"We can state unequivocally that we are talking about deliberate sabotage by the Ukrainian side," Mr Peskov told reporters.

"Apparently, this sabotage is also connected with the fact that, having started large-scale offensive actions two days ago, now the Ukrainian armed forces are not achieving their goals - these offensive actions are faltering."

Read more:
Dam destructions could be most damaging single event of war
Has Ukraine launched a large-scale offensive?
Arms contract shows Iran sold Russia ammunition

Asked about allegations that Russia had destroyed the dam, Mr Peskov said: "We can strongly reject this. We officially declare that here we are definitely talking about deliberate sabotage from the Ukrainian side."

He said the sabotage could "potentially have very serious consequences for several tens of thousands of residents
of the region".

In an interview on Russian state television, Mr Leontyev said: "This crime cannot be written off. This is a terrorist act directed against civilians, Ukrainians did it".

Nuclear nightmare

The dam was built in 1956 on the Dnipro river as part of the Kakhovka hydroelectric power plant and supplies water to the Crimean peninsula and to the Zaporizhzhia nuclear plant, which is also under Russian control.

Ukraine's state atomic agency said the dam's destruction posed a threat to the nuclear plant but that the situation at the facility was currently under control.

"Water from the Kakhovka Reservoir is necessary for the station to receive power for turbine capacitors and safety systems of the ZNPP," Energoatom said in a statement on the Telegram messaging app.

"Right now the station's cooling pond is full: as of 8am, the water level is 16.6 meters, which is sufficient for the station's needs."

"Currently, the situation at the ZNPP is under control, Ukrainian personnel are monitoring all indicators," it said.

The UN nuclear watchdog, the International Atomic Energy Agency, said on Twitter it was closely monitoring the situation but that there was "no immediate nuclear safety risk at [the] plant".

International condemnation

British Foreign Secretary James Cleverly warned that "the destruction of Kakhovka dam is an abhorrent act [and] intentionally attacking exclusively civilian infrastructure is a war crime".

German Chancellor Olaf Scholz said the destruction of the dam was in line with Russia's escalating violence in Ukraine and Russian President Vladimir Putin's strategy of attacking civilian targets.

"For this reason, this is something that has a new dimension but which fits with the way in which Putin wages this war," said Mr Scholz.

EU's top diplomat Josep Borrell said that "Russia's attacks against Ukrainian civilian critical infrastructure reached an unprecedented level today with the destruction of the dam at Kakhovka hydroelectric power plant.

"The European Union condemns this attack in the strongest possible terms. It represents a new dimension of Russian atrocities and may constitute a violation of international law, notably international humanitarian law."