Russian forces have shelled a southern Ukrainian city inundated by flooding in a catastrophic dam collapse, Ukrainian officials said, forcing a suspension of some rescue efforts hours after President Volodymyr Zelenskyy went to the area to assess the damage.

The fresh fighting returned security issues to the region, two days after the collapse of the Kakhovka dam on the Dnieper River set off a scramble to evacuate residents in dozens of flooded areas and get aid to those still there.

Officials on both sides said at least 14 people were killed in the flooding, thousands are homeless and tens of thousands are without drinking water after the collapse. Kyiv accused Moscow of blowing up the dam and its associated hydropower plant, which the Kremlin’s forces controlled, while Russia said Ukraine bombarded it.

The ensuing flooding has ruined crops, displaced land mines, wrought widespread environmental damage, and set the stage for long-term electricity shortages. Exclusive drone footage captured by The Associated Press showed the ruined dam falling into the river and hundreds of submerged homes, greenhouses as well as a church.

Ukrainian President Volodymyr Zelenskyy visits a city hospital with people suffering from flooding in Kherson. Photo / Ukrainian Presidential Press Office via AP

Upriver from the dam, a supply of water used to cool Europe’s largest nuclear power plant was nearing critically low levels, Ukraine’s state hydroelectric company said. The UN’s atomic energy watchdog said work was underway to ensure the Zaporizhzhia Nuclear Power Plant had enough water in reserve to cool its shut-down reactors, in case supplies fell too much.

Zelenskyy’s office said Moscow’s forces also continued to shell Ukrainian-held areas near the nuclear plant, which is under Russian control.

The high water brought new misery and death to a country suffering uncounted casualties after 15 months of war.

Vladimir Leontyev, the Kremlin-installed mayor of Nova Kakhovka, a Russian-occupied city adjacent to the dam, told Russian state TV that five residents there had died in the flooding. Mykolaiv regional Governor Vitalii Kim said one person had died in that region northwest of the city of Kherson.

Yevhen Ryshchuk, the mayor of Oleshky to the south who fled the town after the Russians took over, told The Associated Press that residents told him eight people had died so far in the flooding, with corpses floating to the surface. His tally could not immediately be verified.

Residents of Oleshky have accused Russian authorities in the town of not doing enough to help civilians, and they have formed a group of over 8000 that is sharing messages about information such as stranded and trapped locals.

The Kakhovka dam and station in Ukraine before collapse. Satellite image / Maxar Technologies via AP

In the city of Kherson, the largest municipality affected, Russian shelling echoed not far from a square where emergency crews and volunteers were dispensing aid. Nine people were wounded, including two emergency workers, a policeman, a doctor, and a volunteer from Germany.

As shells landed in floodwaters, rescuers suspended efforts to reach stranded residents and pets in an area that Zelenskyy had visited only hours earlier, officials told AP.

“The strikes began during evacuation of the residents, whose houses were flooded,” Internal Affairs Ministry said. “Russia has abandoned people in calamity in the occupied part of Kherson region. It continues to prevent Ukraine from saving the most valuable — human lives.”

Zelenskyy visited an aid distribution point and a medical facility in Kherson, ordering officials to provide a “fair valuation” of the devastation to compensate residents, his office said in an update.

Russian President Vladimir Putin “has no plans at the current moment” to visit the affected Moscow-occupied areas, Kremlin spokesman Dmitry Peskov told journalists.

Regional Governor Vladimir Soldo, who was installed by Moscow to oversee the area that Russia occupies, accused Ukrainian troops of firing at an evacuation point in Hola Prystan, a Russian-occupied town. Soldo said in a Telegram post that two people, including a pregnant 33-year-old woman, were killed and that two others were wounded. It was not immediately possible to verify his account.

Fighting has intensified along the more than 1000km front line from Kherson on the Black Sea to Ukraine’s border with Russia — in what some experts and officials say could be part of a long-expected Ukrainian counteroffensive. Kyiv has said it won’t announce the start of any such campaign.

Streets are flooded in Kherson after the walls of the Kakhovka dam collapsed. Photo /Libkos, AP

The destruction of the dam prompted the United Nations and local officials to say that the most immediate concerns for affected areas were access to fresh water and avoiding contact with floodwaters contaminated with explosives and industrial chemicals.

Officials say more than 6000 people have been evacuated on both sides of the river. The true scale of the disaster is yet to emerge in an affected area that once was home to more than 60,000.

In areas they control, Russian-appointed authorities said nearly two dozen people have been hospitalised, 4280 people have been evacuated and 14,000 buildings have been flooded.

Russian officials say the dam’s destruction will eventually halt fresh water supplies to southern Ukraine and Russian-controlled Crimea, even though the peninsula has enough fresh water for now, with its reservoirs 80 per cent full.

Ukrainian authorities cut off water supplies to Crimea after Moscow’s illegal annexation of the peninsula in 2014, and Putin cited the need to restore them as the main reason for his decision to invade Ukraine.

Regional Governor Oleksandr Prokudin said about 600sq km of the region were submerged — more than two-thirds of that on the Russian-controlled eastern bank of the Dnieper.

“People are tired ... [they] have no desire to flee to other regions of Ukraine,” Prokudin said.

French President Emmanuel Macron tweeted the dam’s destruction was an “attack” and an “atrocious act”, without assigning blame. Paris said it was rushing aid including water purifiers, 500,000 water purification tablets and hygiene kits.

President Alexander Lukashenko of Belarus, a key Putin ally, said Kyiv blew up the dam to distract attention from what it described as a botched attempt to launch its counter-offensive.

Ukrainian authorities have largely kept quiet about recent battlefield developments amid growing reports of intensified fighting that could add up to the long-awaited counter-offensive.

In a podcast Wednesday, Michael Kofman of the Center for Naval Analyses, a US research group, said fighting had taken a “more qualitative turn” with Ukrainian forces appearing to mount offensive operations near the eastern town of Velyka Novosilka and other points in the southern part of the Donetsk region, as well as on its border with Zaporizhzhia province.

“These attacks I don’t believe to be the main offensive effort, but they mark what I think is the beginning of the Ukrainian offensive,” he said. “This is now beyond shaping operations - they are attacks with multiple brigades, they have dented Russian lines in and around Velyka Novosilka.”

In the eastern Donbas, a battle continued for the largely devastated city of Bakhmut — one of the epicentres of the war. Ukraine’s 3rd Separate Assault Brigade, in a Telegram post, said it was advancing on the city’s flanks.

Russian Defense Minister Sergei Shoigu said his country’s forces drove back Ukrainian troops trying to punch through defensive lines in the Zaporizhzhia region after a two-hour battle involving what he said was up to 1500 Ukrainian soldiers and 150 armoured vehicles.

“The enemy’s reserve forces specially trained for realising this breakthrough did not fulfill their task,” Shoigu said. He did not immediately give evidence for his claims.

Ukrainian armed forces spokesman Valerii Shershen acknowledged “increased activity” in the Zaporizhzhia region, but added he “would not call it something serious”.

- Vasilisa Stepanenko and Jamey Keaten, AP