Sixteen people were killed and about 40 injured after a bus carrying Hungarian students burst into flames on a highway in northern Italy, police and the fire service said on Saturday.

The bus went off the road near a highway exit close to the city of Verona overnight.

The local highway police chief said it was carrying mostly teenage students, teachers and parents.

"Many children among the victims of the accident in Verona, a bus catches fire on impact with a pillar," national police said on Twitter, adding they had come to Italy from France.

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.

He added that there was uncertainty over the exact number of passengers in the bus, but it was higher than the director of the school had known about.

Szijjarto said that one of the victims, whose life was at risk, was being kept in coma, and that all of the injured were in hospital.

The minister added that twelve passengers were "well" and were staying in a hotel in the southern part of Verona.

Local highway police chief Girolamo Lacquaniti told SkyTG24 television some people had minor injuries, but others were more serious.

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."

Police released photographs and television footage of the burned-out hulk near a road bridge. The wreckage had been removed from the road by around 0800 GMT.

"With my prayers, I am with the families and friends shocked by the tragedy," Prime Minister Viktor Orban said in a statement sent to the national news agency MTI.