A bus carrying Serbian tourists veered off the road in Bulgaria early on Saturday as passengers were returning from a holiday in the Turkish resort of Kusadasi, local media reported.
The accident occurred at around 3 a.m., approximately 150 kilometres from the Bulgarian capital, Sofia, according to preliminary information.
The bus was carrying a large group of Serbian passengers, most of them young tourists travelling home after a summer holiday in Turkey.
Most passengers were reportedly asleep when the bus left the road.
Authorities had not immediately confirmed whether anyone was injured or what caused the driver to lose control of the vehicle.
Further information was expected from Bulgarian authorities as they investigated the circumstances and consequences of the crash.