At least 16 people were killed when a bus taking Hungarian school students home from a trip to France was engulfed in a fireball after slamming into a road barrier in northern Italy, police said.

Thirty-nine people survived, though some were seriously injured.

No other vehicles were involved in the crash, and it was not clear why the bus veered into the overpass support column on the road near Verona just before midnight on Friday, said police commander Girolamo Lacquaniti.

The bus was returning to Budapest with students aged 15 to 17. The impact of the crash was so strong that some passengers were thrown out the bus, RAI state radio said.

Sixteen badly burned bodies were pulled from the wreckage. Of the 39 survivors, 26 were injured, some seriously, Mr Lacquaniti said.

The 13 who did not need medical attention were taken to a nearby police station, he said.

In Budapest, the foreign ministry said official information was that there were 54 passengers, including adults accompanying the students, and two drivers aboard, but it believes the actual number was higher - for reasons yet to be determined.

Hungarian Foreign Minister Peter Szijjarto told reporters in Budapest: "One passenger is currently in an induced coma and in life-threatening condition."

He said the bus driver lost control of the vehicle, which hit a guard rail and then the overpass support before catching fire. Investigators found no brake marks at the scene, he added.

RAI state radio said a Slovenian lorry driver, who was travelling behind the bus had noticed a problem with one of the bus wheels and tried to alert the driver.

But the driver didn't react quickly enough, RAI said.