After Russia's worst floods in recent memory swept through the south of the country, thousands of people were last night sleeping in emergency shelters or the ruins of their homes, as anger against the regime of Vladimir Putin grew for failing to give warning of the disaster.

More than 150 people, many of them elderly, died in the floods, after authorities failed to issue warnings or evacuation orders.

The town of Krymsk, home to around 57,000 people, was worst hit, with residents describing how a five-metre (16ft) wave swept through homes in the middle of the night, turning the town into a mudbath. Unlike the dozens of other tragedies that hit Russia every year – from aeroplane crashes to uncontrollable forest fires – anger with Putin's regime was immediate and widespread.

Residents said that even though officials admitted they knew a dangerous flood was coming, they had issued no warning or evacuation order.

"If we had been warned, people could have been saved," said Irina Loskutova, 50, standing in a muddy square near the central market, hoping to gather clothes and food as the city settled into a third night with no electricity. "They knew and they didn't tell us."

Map of Russia's Krasnodar region Photograph: Graphic

According to officials, heavy rains that hit Krymsk and other towns in Russia's Krasnodar region overnight on Friday sent a torrential flood through the city. Residents tell another story: the water came in such volume and at such speed that they are convinced officials purposefully let open the gates on a nearby reservoir, choosing to send its water through Krymsk's winding roads in order to spare Novorossiysk, a nearby port that is the country's largest and whose main harbour facility is owned by allies of Putin. Alexander Tkachev, governor of the Krasnodar region, said during a meeting with locals on Sunday that the first warnings of flooding came in around 10pm on Friday night – four hours before the waters hit. Residents say they were given no warning.

"No one told us anything," said one woman standing at the city administration building, who asked not to be named. "Our officials say the dam had nothing to do with it, but everyone here knows otherwise."

A spokesman for the prosecutor general's investigative committee said the reservoir was not involved in the intense flooding. Local prosecutors earlier admitted the gates had been opened, but it was too early to say if that caused the flooding. Nearby towns were untouched.

As the town's morgues began to fill, refrigerated trucks were parked on the streets outside a nearby hospital to contain the bodies of the dead. Residents are convinced the final toll will reach into many hundreds.

"We'll know how many it really is when the funerals start," said Volodya Lugovoi, 58, sitting on a porch by the city's main stadium, now a vast pool whose pitch is dotted with floating cars.

Handwritten lists of those who had registered as survivors hung outside the municipal youth centre. "I need to find my son's girlfriend," said one man. "He's in the army. No one can find her."

The tragedy has highlighted increasing dissatisfaction with Putin's regime, and growing mistrust of official media as internet use grows. Photos and videos taken on mobile phones revealing the scale of the flood damage spread at lightning speed on social networks throughout the weekend. On Saturday night, state TV news showed Putin flying over the damaged area earlier in the day, but no mention was made of the suffering of flood victims or the anger on the ground.

Putin has ordered officials to investigate whether enough was done to warn people about the floods. But in the absence of a large-scale relief operation, opposition activists – many of whom have been protesting against Putin since he announced his intention to run for re-election – have launched their own efforts to send relief.

"We heard one thing on TV and then saw another on Twitter so we decided to come see for ourselves," said Viktor Chirikov, a volunteer from Novorossiysk.

"The administration here won't help us at all," said Alexey Mandrigelya, 22, another activist.

The emergencies ministry has set up a makeshift camp for some of those who lost their homes in the floods, and local army units are contributing to the effort to hand out water and clothes.

But on the muddy streets of Krymsk, there were no police or government relief workers to be seen.

Many of the dead were elderly. Loskutova described how she saved her 76-year-old mother: "I was screaming, 'Mama mama!' The water came in so fast and hard, we could barely break through the windows. I prayed and screamed for her not to let go."

The two women climbed on top of furniture where they stood until the water almost reached the ceiling, then finally they climbed through broken windows and on to the roof, she said.

"Then I sat with her, wet and naked, for 12 hours on the roof." No emergencies officials came, Loskutova said, and eventually her son arrived with a boat and ferried them to a hospital. "Are we not people?" she asked.

For years, Putin was seen by many as the country's saviour. Now, 12 years after first coming to power, he is increasingly seen as someone overseeing a system that fails to protect its own citizens.

A 39-year old woman who identified herself only as Natalia said she managed to save her six children, her identification papers, and nothing else. "The kids ask me: where will we live? I have no idea what to say. We have no home," she said.

Natalia's house was damaged in the city's last big flood 10 years ago, which residents say was mild compared with the one that struck the region this weekend. "[Officials] told me then they would help me rebuild – I fought for 10 years and got nothing. I went into debt to restart my life. Whatever they say now, I don't believe them – I will never believe them," she said.