The coach, carrying Belgian school children aged around 12 home from a ski trip to Val d’Anniviers in the Swiss Alps, crashed in a tunnel on Tuesday night near the border with Italy.
A senior police officer said: “The coach was travelling at very high speed. It was going considerably faster than the speed limit on a stretch of road where the speed is limited to 100kmh.”
A police photograph showed the bus rammed against the side of the tunnel with the front ripped apart, with broken glass and debris on the road and rescue workers climbing in through windows.
The coach was carrying 52 people, mostly from Lommel and Heverlee in Flanders.
Both coach drivers died in the crash, which injured a further 24 children.
Prime Minister Elio Di Rupo called it a “tragic day for Belgium”.
Parents arrived in Geneva, Switzerland, via military aircraft today, to find out if their children were among those who died.