Twenty-eight people, including 22 children, returning from a skiing holiday died in a bus accident in Sierre in the Swiss canton of Valais, the Swiss news agency SDA-ATS reported on Wednesday.
The children were travelling from Val d'Anniviers and were returning to Belgium.
The bus carrying the passengers was registered in Belgium, the news agency said.
In Brussels, the Belgian foreign ministry said most of the children were aged around 12 and the bus was one of three hired by a Christian group.
The bus was travelling towards Sion, and hit a wall on Tuesday night in the motorway tunnel running from east to west and exiting at Sierre.
Valais cantonal police initially reported only injuries.
The bus was carrying 52 passengers from the cities of Lommel in northeast Belgium and Heverlee near Louvain in the centre of the country.
The news agency said two drivers were killed in the accident.
Four Valais hospitals were treating the injured, SDA-ATS reported. - AFP