Flash floods caused by torrential rain have swept the southern Russian Krasnodar region, killing 144 people, officials say.
The floods, the worst there in living memory, struck at night, reportedly without warning.
TV pictures showed people scrambling onto their rooftops to escape.
President Vladimir Putin has flown over the region by helicopter and has had emergency talks with officials in the worst-hit town of Krymsk.
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.
Russian TV showed thousands of houses in the region almost completely submerged and police said many of the victims were elderly people who had been asleep at the time.
"Our house was flooded to the ceiling," Krymsk pensioner Lidiya Polinina told the Agence France-Presse news agency.
"We broke the window to climb out. I put my five-year-old grandson on the roof of our submerged car, and then we somehow climbed up into the attic."
Dozens of people are reportedly missing, and there are fears that the death toll will rise further.
Emergency teams have been sent from Moscow by plane and helicopter.
Crude oil shipments from Novorossiysk have been suspended.
Regional governor Alexander Tkachev tweeted after flying over the affected area that there was "something unimaginable" going on in Krymsk.
He said, quoted by the Russian Itar-Tass news agency, that "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 reservoir.
But Krasnodar's regional administration dismissed the allegation as "absolute nonsense", Ria news agency said.
The Krasnodar-Novorossiysk motorway was cut, and the transport system in the region is said to have collapsed.
In a statement, the Krasnodar authorities said altogether 13,000 people had been affected by the floods.
They have declared Monday a day of mourning.
'In state of panic'
Up to 1,000 rescuers are involved in searching for victims and evacuating survivors.
More than 7,000 Russian children were attending summer camps in the area and one of the camps was evacuated, Russian media reported.
"The floods were very strong. Even traffic lights were ripped out," regional police spokesman Igor Zhelyabin told AFP news agency, adding that evacuations were under way.
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."
The rains dumped as much as 28cm (11 inches) of water on parts of the Krasnodar region overnight, forcing many residents to take refuge in trees or on house roofs.
Oil pipeline operator Transneft said it had halted crude shipments out of Novorossiysk, but that its infrastructure in the port had been unaffected by the weather.
"Of course, we limited shipments, the port is located in the lower part of town, the whole landslide has moved towards it. As we speak, the rain has started again," spokesman Vladimir Sidorov told Reuters news agency.