(CNN) -- At least 15 people are dead after a tourist boat sunk in a lake in southwest Macedonia on Saturday morning, a government spokesman told CNN.
Three more are said to be in critical condition.
The vessel sunk about 200 meters from the shore in the cold waters of Lake Ohrid around 11 a.m. local time (0500 E.T.), said Ivo Kotevski, a spokesman for the Macedonian Interior Ministry.
"So far we have pulled 15 bodies out of the water, but the search for more casualties is still ongoing," he said.
He said 54 people have so far been rescued from the water and are now being treated in a nearby hotel.
Macedonian authorities don't know the identities of all deceased yet, but a group of Bulgarian tourists are among the dead, Kotevski said.
The waters were calm when the incident happened, but the accident could be due to the boat being overloaded with passengers, Kotevski said.
"The ship, which was made in the 1930s, was examined in May this year. Everything was fine with the ship and it was given a license to operate for another year," said Kotevski.
Police also have video footage of the sinking, because some tourists who were on the shore of the lake filmed the boat going down.
An investigation will be launched into the cause of the accident, he said.
Several senior Macedonian politicians have visited the site of the accident, including the country's president and prime minister, Kotevski said.
Bulgarian authorities have been contacted and they will provide an airplane to bring home the surviving Bulgarians.
Lake Ohrid spans Macedonia's southwest border with Albania and is a popular tourist attraction. The deepest lake in the Balkans, it is known for its natural beauty and fishing.