Federal investigators have said a transformer exploded during repair works, destroying walls and causing a turbine room to flood, while the plant's owner said the accident occured due to a pressure surge in water pipes.
Amateur video of the accident showed an explosion near the base of the dam amid a torrent of gushing water.
Three of the power plant's 10 generating units were completely destroyed, Zubakin said, but Sergei Shoigu, Russia's emergencies minister, said there was no structural damage nor danger that the dam would burst.
Around 1,000 specialists are involved in the search operation around the turbine hall, Russian state television reported on Tuesday.
Shoigu said search teams were "awaiting a robot, which is able to work underwater," to aid the operation.
Electricity supplies from other plants were being routed to areas normally serviced by the station.
Power shortages were reported in the city of Tomsk and the mining area of Kuzbass, the RIA Novosti news agency said.
Andrei Klyuyev, an emergency situations ministry official at the site of the accident, said rescue divers had pulled out one person from a room underneath the plant's turbine hall where there was apparently a cave-in and flooding but said many more could still be trapped.
Russian television showed pieces of concrete, cables and twisted metal pylons beneath the dam wall and the main turbine hall flooded with water and debris.
The natural resources ministry said it was concerned by the environmental impact of the accident, saying an oil slick of more than 25km had spread along the Yenisei River.
"According to preliminary data, transformer fluid has leaked from one of the hydroelectric station's damaged units," the ministry said in a statement.
Analysts have warned that Russia needs to boost its power production significantly to meet the growing demand of industrial producers or it will face regular power shortages.
The country's ageing infrastructure has long been regarded as a key obstacle to Russia's development.