Some 102 people are missing and at least one is dead after a passenger boat with over 180 people onboard sank in the Volga River today, emergency officials said.

The double-decker vessel went down some two miles away from the nearest bank in the giant Kuibyshev reservoir on the Volga River, some 450 miles east of Moscow, the Tatarstan region emergency ministry said.

The depth at the site was 20 metres, it said.

A spokeswoman for the Emergencies Ministry in Moscow, Irina Andrianova said there were 135 passengers and 47 crew onboard when the double-decker went down.

Authorities said a ship rescued some 75 passengers, while the lifeless body of an unidentified woman and one injured man were sent to a hospital.

Russia's Vesti 24 television quoted a survivor as saying that the boat "tilted to the right and sank within minutes".

Emergency teams from neighbouring regions rushed to the site of the tragedy, and Tatarstan's leader Rustam Minnikhanov interrupted his holiday to return to the region.

Earlier, officials said 15 people were missing. It was unclear what caused the discrepancy in the accounts.

An Emergencies Ministry official in Moscow reported a somewhat lower figure. The spokeswoman for the ministry Irina Andrianova said in televised remarks that "the fates of 96 people remain unknown".

The Volga, Europe's largest river in terms of length and discharge, is up to 19 miles wide. The river is a popular tourist destination, especially in summer months. Most of Russia's largest cities are located in the Volga River basin.

The boat, called Bulgaria, was made in late 1950s in Czechoslovakia and belongs to a local tourism company. It was going to the regional capital, Kazan from the town of Bulgar.

A tourism expert said the lack of partitions inside the Bulgaria made it vulnerable to breaches.

"It case of an accident these ships sink within minutes," Dmitri Voropayev, head of the Samara Travel company told the Ria Novosti news agency.