SOFIA, BULGARIA (REUTERS) - At least 45 people, including 12 children, died as a bus carrying mostly North Macedonian tourists crashed in flames on a highway in western Bulgaria on Tuesday (Nov 23), officials said.

Seven people who leapt from the burning bus were rushed to hospital in Sofia and were in stable conditions, hospital staff said. Bulgaria's interior ministry said 45 people died, one less than the toll given earlier.

The cause of the accident was unclear but the bus appeared to have hit a highway barrier either before or after it caught fire, Bulgarian officials said.

Television footage showed the bus charred and gutted by fire in the middle of the highway.

Bulgaria Interior Minister Boyko Rashkov said: "People were clustered inside and were burnt... The picture was terrifying, terrifying. I have never seen anything like that before."

Bulgarian investigative service chief Borislav Sarafov said four buses from a North Macedonian travel agency had entered Bulgaria late on Monday from Turkey.

"Human mistake by the driver or a technical malfunction are the two initial versions for the accident," he said.

The accident happened on Struma highway about 45km west of Sofia around 2am local time (8am Singapore time).

North Macedonian Foreign Minister Bujar Osmani said the coach party was returning to Skopje from a weekend holiday trip to Istanbul.

"This is such a huge tragedy," North Macedonian Prime Minister Zoran Zaev told private television channel BTV.