Weather experts at Germany's weather service Deutscher Wetterdienst warned of heat pollution, as it could feel much hotter than the actual temperature, due to unusually high ozone levels. The affected regions are Baden-Württemberg, Saarland, Rheinland-Palatinate, Hesse and Bavaria.
The heat was only predicted to present a high danger to the health in the far south-west of Germany; in most of the country the danger was rated as medium.
Although it isn't actually exceptionally hot for the time of year, the Deutscher Wetterdienst warned against spending too long outside in the sun, because harmful UV rays were unusually intense.
The south and south-west were urged to exercise particular caution, with the danger to health rated as 'very high' across almost all of the country.
A map of UV intensity. Image: Deutcher Wetterdienst
However, the mini-heatwave is set to come to an abrupt end, with thunderstorms and rain predicted for the weekend.