More than half of the 199 passengers and crew on a tourist boat are feared dead after the vessel sank in Russia.

Cruise ship sinks on Volga River

At least six deaths have been confirmed in the accident involving a double decked tourist cruiser on the River Volga in Tatarstan, about 450 miles east of Moscow.

Dozens of others were rescued from the 55-year-old vessel, Bulgaria, which was sailing from the town of Bulgar to the regional capital of Kazan.

Bad weather, mechanical failure on the aged craft and overcrowding have all been cited as possible reasons why the boat sank while on a two-day cruise.

The 260ft long boat sank several kilometres from the shore near the village of Sukeyevo, south of Kazan, on Sunday afternoon.

About 80 people are reported to have survived the accident, most of them rescued by another pleasure boat that was passing nearby.

But hopes of finding survivors faded as rescuers worked through the night.

Russian President Dmitry Medvedev has ordered an investigation into the incident.