Around 1,400 people have been treated for heat-related problems at the Open Air music festival in canton Valais where temperatures reached 35 degrees Celsius.
The festival said 11 people had to be hospitalised as a result. The event in Gampel had attracted around 85,000 people.
The entire country has been experiencing temperatures between 30 and 35 degrees in a heatwave that is forecast to last until Thursday.
Sion recorded the hottest temperature of the year so far – 35.4 degrees – and the month of August was set to be the fourth warmest on record. The Swiss record for the highest temperature was in 2003 in canton Graubünden where it reached 41.5 degrees.
MeteoSwiss said southwesterly winds were bringing warm air currents from Spain. They added that heatwaves were common in the second half of August, but normally only last up to three days.
Of those seeking respite from the heat, 598 inflatable boats carrying 1,214 people travelled en masse down the Aare river between Kiesen and Bern on Sunday, in what is believed to be a record group journey.
swissinfo.ch and agencies