Overloading is the likely cause of the sinking of the cruise ship Bulgaria on Sunday in Russia's Republic of Tatarstan, a police source said.
"One of the reasons for the cruise ship's sinking could be overloading," the source close to the investigation said.
The two-decked Bulgaria, built in Czechoslovakia in 1955, sank at 13:58 Moscow time (09:58 GMT) near the village of Syukeyevo in the Kansko-Ustinovsky district of the Republic of Tatarstan.
One woman died and up to 110 are still missing, whilst 77 people have been saved, according to the latest information from the regional emergencies center.
The 56-year old vessel had not been renovated, unlike other cruise ships used for voyages down the Volga River, the Russian Tourism Industry Union earlier said.
However Russia's transport watchdog, Rostransnadzor said the vessel was in good technical condition with all the necessary certification. There was "an abrupt sinking of the vessel," Rostransnadzor said.