The bus crashed on a motorway in the village of Bosnek, southwest of the capital Sofia around 2:00 am local time on Tuesday.
More than 45 people were killed, including 12 children, while seven passengers escaped and were taken to hospital with burns. It is not known whether the bus crashed and then burst into flames, or if it caught fire causing the crash, according to a Bulgarian interior ministry official.
The bus was registered in North Macedonia and was mainly carrying tourists returning from Turkey. Officials said the vehicle appeared to have hit a highway barrier and pictures showed a section of the road where the barrier had been shorn off.
The coach, which was carrying mostly North Macedonian tourists back to Skopje, crashed on a highway, causing the deadly inferno. Seven people were taken to hospital in Sofia with injuries. They are in stable condition.
“We have an enormous tragedy here,” Bulgarian interim Prime Minister Stefan Yanev told reporters.
North Macedonian Prime Minister Zoran Zaev said he had spoken to one of the survivors who told him the passengers were sleeping when they were woken by the sound of an explosion.
“I am terrified. This is such a huge tragedy,” he told private television channel BTV.