Russia is observing a day of mourning for the victims of the flash floods in southern Krasnodar region.
At least 171 people were killed in the disaster, officials said on Sunday.
President Vladimir Putin has ordered an enquiry into whether people were given enough warning of the disaster. A separate criminal investigation is under way into possible negligence.
Activists say the floods were worsened by the opening of reservoir sluice gates, but officials deny this.
The day of mourning and enquiry were killed by Mr Putin after he toured the affected area in a helicopter on Saturday.
The 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 houses 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.
"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.
Mr Putin later declared 9 July a day of mourning for those who died in the floods, as well as 14 Russian pilgrims killed in a bus crash in Ukraine on Saturday.
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.
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."
Officials said on Saturday that dozens of people were still missing, and there were 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.
Local activists blamed the ferocity of the flood on the opening of sluice gates at the local reservoir.
The authorities admitted that "automatic discharge" of water had taken place.
However, investigator Ivan Sengerov said it "is still too early" to say whether this was the main cause of the disaster in Krymsk, the Ria Novosti news agency reports.
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.
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.