Thousands more are expected to lose access to food and safe drinking water following the destruction of the Nova Kakhovka dam on the Dnipro River.
Aerial photos show entire streets submerged in the port city of Kherson and rescuers evacuating residents in dinghies.
UN aid chief Martin Griffiths told the Security Council last night that the dam breach “will have grave and far-reaching consequences”.
“The sheer magnitude of the catastrophe will only become fully realised in the coming days,” he said.
Millions of litres of water were gushing through the breached barrier following the “ecocide” attack, which Ukrainian President Volodymyr Zelensky blamed on the “Russian terrorists”.
“The destruction of one of the largest water reservoirs in Ukraine is absolutely deliberate,” he added.
“At least 100,000 people lived in these areas before the Russian invasion.
“At least tens of thousands are still there. Hundreds of thousands of people have been left without normal access to drinking water.
“Our services, all those who can help people, are already involved. But we can only help in the territory controlled by Ukraine.”
A state of emergency has been declared in Russian-occupied Kherson, where the Kremlin-installed leader Vladimir Saldo has said between 22,000 and 40,000 people are affected.
He blamed Ukraine for the explosion. Seven people have been reported missing from the settlement of Nova Kakhovka near the dam.
British defence chiefs also warned on Wednesday that the dam is likely to suffer more damage unleashing fresh flooding.
But the Zaporizhzhia nuclear power plant on the river is unlikely to face “immediate additional safety issues”, the Ministry of Defence said.
They did not explicitly blame Russia for the attack as investigations continue.
Russia’s state-owned RIA news agency said Ukrainian forces dropped dozens of bombs from drones in the border region of Belgorod.
An air raid alert was declared across most of Ukraine this morning.
Andriy Yermak, head of the office of the Ukrainian presidency, reported that two people were killed when a residential building was hit during a drone attack in Sumy in the north east of the country.