Divers on Tuesday searched flooded wreckage for 64 people still missing after an accident at Russia's biggest hydroelectric plant but officials admitted that the chances of finding survivors were dwindling.
The catastrophe at the Sayano-Shushenskaya plant in the Khakassia region of Siberia -- which investigators believed was caused by a sudden increase in water pressure -- is already confirmed to have left 12 people dead.
The pressure increase is believed to have caused a massive flood in the turbine room at a time when a hundred people were working there although investigators have emphasised final conclusions have not been reached.
"Unfortunately we have no comforting news. We still do not know the fate of over 60 people," a grim-faced Russian emergencies situations minister Sergei Shoigu told Russian state television from the region."The territory above water and under the water is being searched. We are awaiting a robot, which is able to work underwater. Three groups of divers are now working under the water," he added.
Russian state television said 1,000 specialists were involved in the search operation.
"It is unlikely that survivors will be found where the flooding happened. We are carrying out search operations," added Vasily Zubakin, acting chairman of the plant's operator RusHyrdro, according to Russian news agencies.
He confirmed that 64 people were still unaccounted for.
He said it was highly unlikely that the accident, caused by a rupture of water pipes in one of the plant's power units, was due to any kind of terror act, saying "we regard a technical breakdown as the cause".
Vladimir Markin, a spokesman for the investigative committee of prosecutors, also said investigators "had not found any explosive substances at the scene of the disaster" and ruled out terror as an explanation.
But he said that a criminal inquiry had been opened for neglecting the rules of safety at work.
Local officials have said that Wednesday will be an official day of mourning in Khakassia, a remote region in the mountains of southern Siberia.The power station is one of the most powerful in the world with a capacity of 6.4 million kilowatts an hour.
The components were undergoing repairs when the accident occurred, causing a large portion of the power unit to break off and puncture the ceiling and wall, allowing water to pour in and flood the chamber, officials said Tuesday.
The accident sparked panic among nearby residents who feared the massive dam at the facility might collapse, but officials said there was no threat to people downstream.
Rescue divers had on Monday pulled out two people alive who were suffering from hypothermia but were otherwise unharmed.
The accident disrupted power supply to key smelters in the region including those of UC Rusal, Russia's largest aluminium producer, and other enterprises.
Russia's financial regulators ordered the suspension of trading on both Moscow stock exchanges in shares of state-run RusHydro, the corporation that owns the damaged hydroelectric station.
Rebuilding the plant will take four years at a cost of 10 billion rubles (222 million euros, 314 million dollars), Zubakin said. Three generators were ruined although the massive dam remains intact.
Officials also warned that the price of electricity in the region would increase as a result of the shortfall left by the hydro-electric plant and an increase in energy from coal.
The natural resources ministry has also said it was concerned by the natural resources ministryof the accident, saying an oil slick of more than 25 kilometres (15 miles) had spread along the Yenisei River.