“Shortly before 4:00 pm (1400 GMT), for reasons which remain to be determined, the aircraft collided with the northern slope in the area of Fluhalp,” near the mountain resort of Leukerbad, the Valais cantonal police said.
All three passengers aboard perished, the police said, adding that they were working to identify the victims.
After taking off from Lugano in the southern Italian-speaking canton of Ticino, the aeroplane made a stop in the Valais city of Sion before heading off towards the Buochs aerodrome in the central canton of Nidwalden.
The federal Swiss authorities have opened an investigation into the causes of the accident.
