Russian rescuers recovered nearly 50 bodies on Monday from an overcrowded pleasure boat that sank in the Volga River in an accident the Kremlin blamed on disregard for safety.

Divers reported raising 48 bodies off the vessel, the Bulgaria, which went down in a heavy storm on Sunday on one of Russia's main rivers with 208 people on board.

Only 80 people were rescued in the first moments after the accident and no one was found alive on Monday, despite an all-night search involving dozens of divers, support vessels and helicopters.

Stunned relatives huddled in a group near the shore waiting to hear about their l

oved ones, though hope was in short supply amid reports that at least 30 children may have disappeared on the sunken 56-year-old craft.

President Dmitry Medvedev proclaimed Tuesday a day of national mourning and demanded a complete review of all Russian transport.

"We have enough old tubs floating around," Medvedev sternly told a government meeting in reference to outdated vessels.

"Based on the information we have today, the ship was in an unsuitable condition," Medvedev said in nationally televised remarks.

"We can already say today that the accident would not have happened had the safety requirements been met... despite the weather conditions."

One of Medvedev's top ministers told the government meeting that the craft was filled well beyond capacity when it sailed in breach of basic regulations from the central Russian city of Kazan, about 800 kilometres (500 miles) east of Moscow.

"All the witnesses that were on the boat have been questioned, we found out that there were 208 people on board," emergency situations minister Sergei Shoigu was quoted as telling Medvedev.

Officials had earlier said that the ship was not designed to carry more than 140 people.

"Unfortunately, after divers examined the boat we can say that finding survivors there is practically hopeless," the emergencies minister said.

Investigators said that the ageing vessel had engine trouble even before setting out on the cruise and was seen to be listing to one side.

"Even before it left (its home port) Kazan, the boat had a problem with the main left engine, but went out to the cruise nevertheless," transport investigators for the Volga region said on the official website.

Russia's General Prosecutor said in a statement that the ship was last retrofitted three decades ago and didn't even have a license. "There was no license to carry passengers," the prosecutor's office said on the website.

The transport ministry earlier said that the ship was reviewed in mid-June and its technical condition was deemed suitable.

But officials said the boat sank too quickly to use the two lifeboats on board because it filled with water and went down within minutes.

"We are hoping that there are remaining pockets of air where people can breathe," head of Volga region emergency ministry branch Igor Panshin on state television.

"If the hold was open, then water went inside very quickly as the boat turned over" before people had the chance to run to the upper deck, said ministry spokeswoman Svetlana Lebedeva said.

Several weeping survivors draped in thick blankets said lives were lost because some passing boats never stopped to help.

"Two boats went by without stopping, even though we waved and waved," said survivor Nikolai Chernov on state television.

The death toll of more than 40 already makes the Bulgaria disaster the biggest in Russia since the ship Admiral Nakhimov sunk in 1986 drowning 423 in the Black Sea.

Built in 1955 in what was then Czechoslovakia, the Bulgaria was nearly 60 years old, which is unacceptable but quite typical for Russia's river fleet, said the spokeswoman for the Russian tourism industry Union Irina Tyurina.

"All the ships that navigate Russian rivers are extremely old, and no new ones are being built," she told AFP.

The same kind of vessels are now used from rivers in Ukraine to distant parts of northern Siberia.