The dead and injured were among a Belgian school group returning home after a ski holiday, according to the Valais cantonal authorities.
Twenty four children were injured. There were 52 people in the coach.
The group comprised two school parties from Flanders. They had been staying at a ski resort in Val d’Anniviers. The children were between ten and 12 years old.
The bus was travelling from Sierre to Sion through a tunnel on the A9 motorway, when for unknown reasons it veered and slammed head first into the tunnel wall.
The alarm was raised just after 9.15pm. More than 200 people were involved in the rescue operation, including 15 doctors, 30 police officers and 60 fire officers. It took more than eight hours.
The authorities told a news conference that the two drivers on the coach had been killed in the crash.
Most of the injured have been taken to four hospitals in the area with three seriously injured transported to the university hospitals in Lausanne and Bern.
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