Thirty-five people, including seven children, were missing in southern Ukraine on Sunday following devastating flood prosecutors called the "worst environmental catastrophe since Chernobyl."

The Russian-controlled Kakhovka dam along the front line in the Kherson region was destroyed on June 6, forcing thousands to flee and sparking fears of humanitarian as well as environmental disasters.

Ukraine accuses Russia of blowing up the dam on the Dnipro River, while Moscow says Kyiv fired upon the structure.

Ukrainian interior minister Igor Klymenko said that 77 towns and villages had been flooded in the southern regions of Kherson and Mykolaiv.

Klymenko said that in the Kherson region 35 people were missing, including seven children.

As a result of the flood, five people died in the region of Kherson and one person was dead in the region of Mykolaiv.

A total of 3,700 people have been evacuated from their homes in the two regions, the minister added in a statement.

Separately, Ukrainian Prosecutor General Andriy Kostin and representatives of the International Criminal Court visited the flooded territory, his office said.

"This is the worst environmental catastrophe since Chernobyl so we are investigating not only a war crime but also an ecocide," Kostin said in a statement.

"The situation is very complicated," he added.

He noted that a number of "dangerous" facilities including at least three cemeteries, oil storage terminals and garbage dumps have been flooded.

A total of 450 tonnes of turbine oil have spilled into the waters of the Dnipro and the Black Sea, he said.

More than 170 prosecutors have been investigating the breach of the dam.

"Our colleagues from the International Criminal Court are also with us," he s