Bulgarian Caretaker Prime Minister Stefan Yanev visited the site of the bus crash which killed at least 45 people on Tuesday and told reporters it was "a huge tragedy".
"I take this opportunity to send my condolences to the relatives of the victims," Yanev said.
The bus, registered in North Macedonia, crashed in Bosnek, near the capital Sofia, at about 2 a.m. (midnight GMT) and there were children among the victims, authorities said. Seven people were taken to hospitals for treatment.
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The cause of the crash was not immediately confirmed, but it appeared that the bus hit a highway guard rail, crashed and caught fire.
Officials said an investigation would be launched.
Bulgarian news agency Novinite said representatives from North Macedonia’s embassy visited a hospital where some of the victims were taken.
In 2019, Bulgaria, an EU nation of seven million, had the second-highest road fatality rate in the 27-nation bloc with 89 people killed per million population, according to European Commission data.