Divers searching for victims in a sunken tourist boat in Russia's Volga River have found approximately 40 children, the highest death toll for children in Russia since a 2004 terrorist attack.

Divers visually estimated most of the nearly 50 corpses found after the Bulgaria sank late Sunday evening were children, though they have not begun removing bodies from inside the ship. According to the New York Times, 59 of the 208 on board were children, most of which frequented the recreation room, where divers expect to find the remainder of youth casualties.

While 80 passengers were found in an hour and a half and recused the fatalities amass to 63 people, with 64 still missing, as reported by Al Jazeera. According to a survivor, two cargo barges passed before the Arabella rescued those floating in the water amidst the debris. A day of mourning is scheduled for today in Russia.

While the cause of sinking is still yet to surface, President Dmitri Medvedev ordered investigation to find out why the boat suddenly tipped along the Volga River. Reports show that the Bulgaria tilted starboard before inevitably sinking, possibly due to its overload. The boat, carrying 208 passengers, was jammed with 75 percent more passengers than it was capable of holding safely though it is unknown if this is the definite reason for the sinking.

It is, however, known that the boat was experiencing engine trouble due to a defunct left engine as it left Bulgar heading to Kazan, according to the Investigative Committee. Russian news agency Itar-Tass reported that some passengers expressed concern about the tilt before the liner had set sail, asking Captain Aleksandr Ostrovsky to cancel or delay the trip. Capt. Ostrovsky, who has yet to be found, reportedly refused.