An overloaded sightseeing boat carrying dozens of Bulgarian tourists sank Saturday in a lake on Macedonia's western border, and 15 people drowned, officials said.

The vessel, called the Ilinden, sank rapidly in just 20 feet of water in Lake Ohrid, police spokesman Ivo Kotevski said. The vessel split in two and sank about 650 feet from shore.

There were 57 passengers on board, Kotevski told The Associated Press. Of those, 15 drowned and 42 were rescued. Four passengers who were recovered unconscious are still in hospital but are not in danger, he said.

Earlier reports had put the number of passengers on the Ilinden at 73. Police later corrected the number.

"The 23-year-old skipper and his deputy have been questioned about the incident. In their first statements they said that a loud crack was heard (toward the rear) before the boat sunk rapidly," Kotevski said.

One witness said she and others rushed to the scene in a speedboat.

"The scene was horrible," Gordana Ruvcevska said. "We saw at least 10 bodies floating. We pulled out three survivors."

Most of the passengers on the 70-year-old boat, which had a 42-person capacity, belonged to a group of tourists from Bulgaria.

The vessel had been traveling from Ohrid, on the lake's eastern shore, to the medieval Eastern Orthodox monastery complex Sveti Naum about 20 miles south near the Albanian border, according to Macedonia's private A1 television. Lake Ohrid itself — the deepest in the Balkans, located along the mountainous border between Macedonia and Albania — has been a UNESCO world heritage site since 1979.

Macedonia's government held a special meeting Saturday and declared Sunday a day of mourning. Transportation Minister Mile Janakievski offered his resignation.

"This is the worst accident that has ever happened on the Ohrid Lake," police spokesman Stefan Dimoski told The Associated Press.

A Bulgarian government delegation, headed by Health Minister Bozidar Nanev, arrived in Ohrid, Macedonian media reported. Bulgarian Prime Minister Boiko Borisov has sent a government plane to pick up the survivors.