Montenegro Interior Minister Rasko Konjevic said the bus with 46 people on board crashed some 30 kilometers (18 miles) north of the capital, Podgorica. He said the bus was traveling from Romania to Montenegro's Adriatic coast.
Police said the bus plunged from a bridge over the Moraca river during a rain storm and crashed some 40 meters (130 feet) into the ravine. A helicopter was used in the rescue operation mounted by Montenegro police.
Konjevic said "sadly, this death toll could climb further" because seven of the passengers were seriously injured.
The winding road that leads from Serbia in the north through the Moraca canyon and then to the seacoast is notorious for traffic accidents because it is narrow and slippery in wet weather conditions.