A bus crash in western Bulgaria early Tuesday morning has killed at least 45 people, authorities say. The bus, which was registered in Northern Macedonia, crashed around 2 am and there were children among the victims, authorities said. Seven people were taken to hospitals for treatment.

The cause of the crash was not immediately clear. Officials said an investigation will be launched. Bulgarian news agency Novinite said representatives from Macedonia’s embassy visited a hospital where some of the victims were taken.