Russian authorities said Monday that 48 people had been confirmed dead in Sunday's ship sinking tragedy in the Volga River.

Emergency officials cautioned that the death toll might rise as rescuers were salvaging more bodies from the shipwreck and that the 80 people that were missing had small chances of survival.

Russian Emergencies Minister Sergei Shoigu told President Dmitry Medvedev at a Monday meeting that there might be 208 people aboard the double-decker cruise ship named "Bulgaria."

"We questioned all the witnesses who traveled on that ship. It appeared that the ship was carrying 208 people," Shoigu said, adding that "25 passengers were not registered and we still need to find out how they got on."

Earlier information from the Emergencies Ministry said that there were 185 people aboard, among whom 80 were rescued and some 100 others were missing.

Ministry spokeswoman Irina Andrianova conceded that chances of finding more survivors were "very small."

Also on Monday, Medvedev declared Tuesday a day of national mourning.

The 56-year-old ship sank at 1:58 p.m. Moscow time (0958 GMT) Sunday near the village of Syukeyevo in the Kansko-Ustinovsky district of the southwestern Russian republic of Tatarstan.

According to the Russian Transport Ministry, the ship was not allowed to transport passengers and the shipowner did not acquire a license for the voyage.

Meanwhile, the Investigation Committee (IC) in Moscow said one of the cruise ship's engines was in bad shape before sinking into the longest river in Europe.

"Initial investigative procedures showed that the vessel had a left engine defect but went on the voyage nevertheless," the IC was quoted by the Interfax news agency as saying.

"It also appeared that the vessel tilted to the right when it departed,"the IC said, adding that "open portholes on the lower deck could be another reason why river water poured inside."

Earlier, Interfax quoted rescuers as saying that about 110 bodies, including 30 children, had been found inside the wrecked ship.

A survivor told reporters that there were many children aboard, and the vessel sank only eight minutes into its journey.