It was a Soviet engineering marvel, a concrete monolith soaring above the canyon, harnessing the might of the Yenisei River to generate power for a swath of southern Siberia.

Today, the dam forming the backbone of the Sayano-Shushenskaya hydroelectric plant is an equally potent symbol of decline, a vital energy source transformed into a watery graveyard and painful reminder of Russia's infrastructure woes.

"We never imagined something like this could happen," said Nina Moskvitinka, 62, a resident of the town of Cheryomushky where many of the station's many hundreds of employees reside.

She recalled the town's pride when construction began in the 1960s on the plant, Russia's largest and among the most powerful on earth with capacity of 6.4 million kilowatts an hour, three times that of the fabled US Hoover Dam.

"It is frightening, of course. But we have to bury our fear," Ms Moskvitinka said.

"What would we do without the plant? It is the heart of the region."

That heart however failed spectacularly when a technical mishap during repairs triggered a surge of water pressure that ruptured a generator, destroyed retaining walls and sent water flooding into the turbine hall.

A large portion of that hall, at the base of the dam, is now a yawning cacophony of twisted metal, ruptured pipes and fractured slabs of concrete poured when the Soviet Union was at the zenith of its technical prowess.

And much of it is under as much as 20 metres of water, where the bodies of 56 plant workers still missing after the accident may be located.

Nineteen people have been confirmed dead in the accident.

"The weight of the water was so heavy and so intense that in mere minutes it surged up 20 metres," said Andrei Mitrofanov, the plant's head engineer who is now helping direct search and rescue efforts.

"It was such a powerful blow," he said, pointing upwards to where there was once a ceiling above the station's turbine room.

"I cannot describe it anymore. I don't want to think about it."

His words are almost inaudible above the screech of electric saws slicing through heaps of metal, part of the effort by 2,000 helmeted search and rescue workers to locate survivors, salvage corpses and clean up the surreal mess.

Prime Minister Vladimir Putin acknowledged that the catastrophe at the Sayano-Shushenskaya hydroelectric plant represented a much more extensive problem with the infrastructure Russia inherited from the Soviet Union.

"There is a need to conduct serious inspections of all strategic and vitally important objects of infrastructure," Mr Putin said at a government meeting in Moscow last week.

"The recent tragic events at the Sayano-Shushenskaya hydroelectric plant showed with all clarity how much more we should do to increase reliability of technical constructions on the whole."

But as rescuers continue their work at the stricken plant, water continues to flow unchecked through the wrecked and now silent turbines and officials say it will be several years before the facility can be fully repaired.

Three rescue boats ply slowly through the lake formed at the foot of the 245-metre dam, fielding teams of divers who have been searching round the clock for survivors in the near-freezing water.

"They had no safety plan," said Natalya, one of around 1,500 local residents who turned up in a Cheryomushky public square for the funeral of six workers killed in the disaster.

"People did not know where to run. It is a terrible situation and we will not forget it soon."

As investigators begin to probe the technical reasons for the accident, witnesses and survivors recount their own experiences.

One man says he was at the plant the moment the accident occurred and regained consciousness only to find himself washed up along the riverbank several kilometers downstream from the dam.

Another says he saw an "elephant-sized" rotor weighing several tonnes burst through the thick steel encasing of the wrecked turbine and fly into the air, followed by a wall of water that came crashing down into the chamber.

Another local woman present at the funeral, Lyuba Odeyeva, said her son Igor, an employee at the station, was on duty when the accident occurred but declined to attend the ceremony in order to help with the search effort.

"He swam out with three others," Ms Odeyeva explained.

"They were in bad shape after the cold water. But he only took the time to come home and have a shower before going back to work to assist in the search," she said.

Soviet-era banners still standing along the road to the Sayano-Shushenskaya plant boast with communist-period triumphalism of what was then the facility's state-of-the-art technology and extraordinary power-generating capacity.

Top officials on the scene this week however, notably Emergency Situations Minister Sergei Shoigu, are only able to offer reassurances that the once-great power station will eventually be restored to its former glory.

They have not however, explained to the satisfaction of inhabitants of the region served by the plant, how the energy shortfall will be made up in the meantime without a dramatic increase in electricity prices.