Geneva recorded its hottest 23 June on record yesterday, hitting 36, shattering the previous mark of 35.6 set in 2003.
Payerne reached the same level, while Zurich, Chur and Lucerne all climbed past 33.
MeteoSwiss says the run of tropical days will be unusually long, with no real relief expected before the weekend.
Authorities are urging residents to drink plenty of fluids, seek out cool places and check on the elderly as the heatwave shows no sign of breaking.
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Copernicus reports hottest summer ever measured
Switzerland is in the grip of a level 3 heat alert, with Geneva heading for temperatures of up to 36°C on Friday.
Tough new banking rules possible
The Federal Council has launched consultations on new banking rules that could withhold or claw back bonuses from top banking executives.
Speed crackdown affects all of Switzerland
The Federal Council has tightened the rules for imposing 30 km/h zones on city streets, requiring cantons to prove that a slowdown will not push traffic into residential neighbourhoods
Back to school concern over heat
Vaud is preparing to map every school building in the canton to identify the classrooms most vulnerable to extreme heat
Eye warning for eclipse watchers
Anyone who watched Wednesday's solar eclipse without proper glasses should watch for signs of retinal damage, doctors are warning
