Regional authorities in Switzerland temporarily cut bus and train fares Saturday to encourage people to leave their cars at home, as a scorching heatwave sent ozone pollution levels soaring.

In Geneva, all public transportation was available at reduced rates, the regional environment department said, adding that the lower prices would continue until the ozone levels were back to normal.

"Considering the ozone spike..., car and motorbike drivers across Geneva are asked to choose public transportation, and benefit from reduced rates," it said in a statement.

The measure, aimed at reducing vehicle-driven pollution, means a bus or tram ticket in the Swiss city will cost 2.00 Swiss francs instead of three.

In neighbouring Vaud and Valais, where ozone levels have also been unusually high, authorities meanwhile decided to offer a rebate on train discount cards.

Switzerland, like a range of other European countries, has in recent days been facing a searing heatwave, with temperatures as high as 38 degrees Celsius (100 degrees Fahrenheit).

The heat is driving an increase in pollution, with ground levels of health-hazardous ozone soaring well above the normal average of 120 microgrammes per cubic metre (?g/m3) in several Swiss regions, reaching as high as 260 (?g/m3) in the south.

Pointing out that ozone can cause respiratory symptoms like irritating airways and provoking asthma attacks, regional authorities also warned against sports and other intense physical activity outdoors, and against smoking.