A view shows the site where a bus with North Macedonian plates caught fire on a highway in Bulgaria. Reuters

At least 46 people, most of them tourists from North Macedonia, died as a bus crashed in flames on a highway in western Bulgaria on Tuesday, officials said.

"Forty-five or 46 people were killed" on a highway about 40 kilometres (26 miles) from Sofia, Nikolay Nikolov, head of the Fire Safety and Civil Protection department at the interior ministry, told public broadcaster BNT.

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"Seven passengers were saved" and taken to a hospital in the capital, he added.

Children were among the victims, and seven survivors needing treatment for burns were rushed to hospital in the capital Sofia, Bulgarian interior ministry senior official Nikolai Nikolov told private BTV television.

Members of the media stand close to the site where the bus caught fire on a highway in Bulgaria. Reuters

The cause of the accident has yet to be determined.

The accident happened on Struma highway about 45km (28 miles) west of Sofia around 2am (0000 GMT). The site had been sealed off and Bulgarian interim Prime Minister Stefan Yanev rushed to the scene of the tragedy.

An official from Sofia emergency hospital said the seven people receiving treatment has jumped out of the burning bus. All were in stable conditions.

North Macedonian Foreign Minister Bujar Osmani said the coach party was returning to Skopje from a weekend holiday trip to Istanbul, Turkey. (Reporting by Tsvetelia Tsolova; Writing by Stephen Coates; Editing by Simon Cameron-Moore)

Firefighters are seen at the site of fire in Bulgaria. AP

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 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.