An explosion thought to have been caused by a pressure surge in water pipes at Russia’s largest hydroelectric power station, the 6,400-MW Sayano Shushenskaya plant in southern Siberia, on Monday killed at least 12 people and injured scores of others. Dozens more are feared dead as a result of the accident.

The plant’s owner, state-owned RusHydro, said in a statement that a “powerful shock”—the cause of which is still under investigation—destroyed three of the plant’s 10 generating units. The second turbine at the hydropower plant was completely destroyed, while the seventh and ninth turbines suffered extensive damage. The company stressed that there was no structural damage and no danger that the dam would burst.

At least 12 people were killed and 14 injured when water burst into and flooded the main turbine room of the giant plant on Monday. About 64 people are thought missing, but hopes were fading Tuesday that any of these workers would be found alive.

Alexander Toloshinov, a manager for RusHydro and a former director of the plant, said that because of chilly water temperatures, survivors could only be expected if they were lucky enough to be in an “air bubble,” The Moscow Times reported.

Toloshinov also reportedly said that a technical fault in a turbine was to blame for the disaster. “A turbine was destroyed, and indicators show that this was not caused by the water surge but by a broken turbine lid,” he said.

The accident cut power supplies to homes and companies, including metal giants Evraz Group and RusAl, forcing them to switch to emergency power. Six factories in the nearby Altai region also reportedly shut down due to the electricity shortage. The damage will cost at least 10 billion rubles and take up to 20 months to fix, RusHydro officials said.

The plant in the Khakassia was a landmark project when it was completed in 1978. It straddles Siberia’s Yenisei River and features a 245-meter-high concrete dam that holds a water reservoir stretching over 621 square kilometers, says RusHydro’s website. But according to Reuters, though the station produced three times as much power as the Hoover Dam, its turbines had not been overhauled since Soviet times.

RusHydro was set up in December 2004—when the country was reforming its electric power industry—to ensure reliable and safe operation of 15 federal hydropower plants, among them, the giant Sayano-Shushenskaya plant. Hydropower development in Russia had virtually stagnated in the 1990s, and existing plants were—and continue to be—in bad shape, RusHydro says on its website.

“The equipment of most Russian hydro-plants is over 40% obsolete and for some [hydropower plants], this figures reaches 70%, this being connected with the system-wide problem of the entire hydropower industry of the last fifteen years—chronic underfinancing,” it says.

Sources: RusHydro, The Moscow Times, Reuters