About a dozen children were on the bus as seven passengers were saved and taken to a hospital, interior ministry says.
At least 45 people were killed in an overnight bus accident on a highway south of the Bulgarian capital.
The cause of Tuesday’s accident on a highway 40 km (26 miles) from Sofia has yet to be determined.
"Forty-five or 46 people were killed,” Nikolay Nikolov, head of the fire safety and civil protection department at the interior ministry, told public broadcaster BNT.
"Seven passengers were saved” and taken to a hospital in the capital, he added.
According to the bTV channel, 12 children were onboard the bus, which was travelling from Turkey’s main city of Istanbul to Skopje in North Macedonia.
Prime Minister Zoran Zaev, who reportedly intends to come to the scene of the crash, said the victims were probably fellow Macedonians.
"We don’t know if all the victims are from North Macedonia, but we assume so because the bus is registered in the country,” he said in an interview with Nova TV.
The state prosecutor’s office has launched an investigation.