SIXTEEN people were killed and more than two dozen injured when a bus carrying Hungarian students burst into flames on a highway in northern Italy.

The vehicle, was carrying students aged between 15 and 17, teachers and parents, crashed into a highway barrier and burst into flames.

Six adults were seriously injured and are being treated in hospital in Verona, two of whom are in a "life-threatening" condition.

There were no other vehicles involved in the crash near Verona and it is not yet known why the bus, which was on its way to Budapest, left the road.

The number of victims could rise to 18, "but certainly no more than that", the Hungarian consul in Italy Judit Timaffy said.

Hungarian Foreign Minister Peter Szijjarto told a news conference that the teenagers were from a Budapest secondary school, returning from their annual ski camp in France.

A spokesman for the minister said the school was the Szinyei Gimnazium and the school’s director, Gabor Toth, said the official passenger list included 54 people.

Toth said there were 36 students on board, some former students, three teachers and the family of one of the teachers.

A physical education teacher, who suffered severe burns, returned to the bus several times to save other passengers and all of the survivors were "well taken care of" with nobody suffering life-threatening conditions, said Timaffy.

All of the injured were in a Verona hospital and 12 other passengers, who were “well”, were staying in a hotel south of the city, the minister said.

Local highway police chief Girolamo Lacquaniti said the cause of the crash would be investigated: “We are not aware of other vehicles being involved, it seems to have gone off the road of its own accord.”

Hungarian Prime Minister Victor Orban said, “With my prayers, I am with the families and friends shocked by the tragedy,” .

Italian Prime Minister Paolo Gentiloni called Orban to express his condolences.