The coach, carrying 45 passengers, was travelling between Susch and Zernez in the Graubünden region when it hit a safety barrier in a roadworks area, left the road and overturned late on Thursday afternoon, according to police.
Rescue teams, including several helicopters, were deployed to the scene. Police said on Friday that the deceased had not yet been publicly identified and that the injuries among the survivors ranged from serious to minor.
The coach had reportedly left the Netherlands on Monday and was on a day trip to Switzerland from Austria when the accident occurred. The tour operator was identified as OAD.
Dutch Prime Minister Rob Jetten expressed his concern for all those involved, while King Willem-Alexander and Queen Máxima said their hearts went out to everyone affected by what they called "this great tragedy."
Swiss President Guy Parmelin posted on X that he was "deeply shocked" by the incident and offered his "sincere condolences" to the families of the victims.