VERONA, Italy -- The Hungarian students had just a week of skiing in France when their bus swerved right, left, hit a highway barrier and burst into flames.

Sixteen people were killed and over two dozen injured in a tragedy that sparked a national day of mourning in Hungary.

The impact of the crash just before midnight Friday on the northern Italian highway was so violent, the overpass support column entered several rows into the bus, officials said Saturday.

The ensuing fireball burned some of the 16 dead beyond recognition and torched the bus, leaving a skeleton of twisted steel.

No other vehicles were involved in the crash near Verona, and the cause wasn't known, said a tearful police commander, Girolamo Lacquaniti.

Of the 39 survivors, 26 were injured, some seriously, he said. Hungarian Foreign Minister Peter Szijjarto said in Budapest one passenger was in an induced coma.

"The fire was so huge, it took up practically half of the three-lane highway," said Lanfranco Fossa, a businessman who stopped to offer help when he realized some injured youths had escaped the flames.

"These poor creatures, almost all of them were in short sleeves, some without shoes," he said. "I gave them what I had: a shirt, a blanket. And others stopped to give them things as well."

Fossa said he also offered the children his cellphone so they could call home to Budapest. He stayed over an hour to help translate for rescue crews, helping them find the most severely injured and understand what had happened. The students all spoke excellent English, but the rescuers didn't.

Fossa wasn't the only hero. One teacher on the bus saved some of the kids, suffering serious burns to his back as he did so, said Judit Timaffy of Hungary's consulate, who was at the scene.

And one student smashed open a bus window with the emergency hammer.

"The kids told me that the fire started, and they escaped from the fire, breaking the windows of the bus," she said. "Some of them managed to escape, but many were left inside."

In Budapest, the government declared a day of national mourning for Monday, with flags to be flown at half-staff and schools around the country holding commemorations.

A black flag flew Saturday above the entrance to the Szinyei Merse Pal high school in Budapest. A few hundred students and parents gathered for a vigil outside the school, some of them weeping, lighting small candles and laying flowers in memory of the victims.

"We knew many of them, but the ones we were closest to and in daily contact are mostly all right," student Tamas Mezo said after placing candles at the school's door.

He said the school organized a ski camp each year, involving about 50 to 60 students and a few teachers.

"I was very much planning on going this year but in the end it didn't work out," Mezo said. "There were three or four teachers on the bus, and unfortunately one of them did not survive. Our hearts are hurting because we loved him."

Szijjarto said the bus driver lost control of the vehicle. Investigators found no brake marks at the scene, he said. Timaffy said investigators were looking into the possibility the driver fell asleep at the wheel.

RAI state radio said a Slovenian truck driver traveling behind the bus had noticed a problem with one of its wheels and tried to alert the driver. But the driver didn't react quickly enough, RAI said. The Slovenian truck driver stayed at the scene to help until investigators arrived.

By Saturday afternoon, the survivors had been taken to a nearby hotel and were being interviewed by investigators, the ANSA news agency reported. The parents of some of the students were heading there to bring them home.

Condolences to Hungary came in from Italy's president and its foreign minister, as well as the German chancellor.