Russian President Vladimir Putin has ordered an inquiry into whether enough was done to prevent mass deaths in the southern flood-hit Krasnodar region.
After personally inspecting the area, Mr Putin said he wanted to know how much warning local residents had been given about the impending disaster.
At least 144 people were killed, with some activists blaming the ferocity of the flood on the opening of sluice gates at a reservoir.
The local authorities deny the claim.
“The investigative committee will check the actions of all the authorities – how the notice was given… how it should have been given and who acted how,” Mr Putin was quoted as saying by the Itar-Tass news agency at a meeting in Krymsk – the worst-hit town.
He was speaking after flying over the region by helicopter to see for himself the damage that followed torrential rain.
It was the first major disaster in Russia since Mr Putin, 59, returned for a third-term earlier this year, after a four-year term as prime minister.
Flash floods, the worst there in living memory, struck in the Krasnodar region on Friday night, reportedly without warning.
The rains dumped as much as 28cm (11 inches) of water overnight, forcing many residents to take refuge in trees or on house roofs.
TV pictures later showed thousands of house almost completely submerged with people scrambling onto their rooftops to escape the rising waters.
Most of those who died were in and around Krymsk, a town of 57,000 people. But nine deaths were reported in the Black Sea resort of Gelendzhik with a further two in the port town of Novorossiysk.
Anna Kovalevskaya, who says she has relatives in Krymsk, told the BBC her family was caught unawares by the floods.
“The water started flooding in at 02:00 [22:00 GMT Friday],” she said.
“People were running out into the streets in their underwear and wrapping their children in blankets. People were only able to save their passports.
“There is no electricity and the shops are shut. Many people have lost everything and are in a state of panic.”
Dozens of people are reportedly missing, and there are fears that the death toll will rise further.
Regional governor Alexander Tkachev said: “No-one can remember such floods in our history. There was nothing of the kind for the last 70 years”.
Some users of social media networks in Russia said Krymsk looked like it was hit “by a tsunami”. Others accused the authorities of not telling the whole truth about the disaster.
The head of the liberal opposition Yabloko party, Sergei Mitrokhin, said on his Twitter feed that local activists had blamed the ferocity of the flood on the opening of sluice gates at a local reservoir.
But Krasnodar’s regional administration dismissed the allegation as “absolute nonsense”, Ria news agency said.
The Krasnodar authorities said altogether 13,000 people had been affected by the floods.
More than 7,000 Russian children were attending summer camps in the area and one of the camps was evacuated, Russian media reported.
Up to 1,000 rescuers are involved in searching for victims and evacuating survivors.
Monday has been declared a day of mourning.
Oil pipeline operator Transneft said it had halted crude shipments out of Novorossiysk – a major port on the Black Sea.
But the company added that that its infrastructure had been unaffected by the weather.
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