The temperature at national weather centre De Bilt near Hilversum was over 25 degrees Celsius at 12 noon on Friday, making the heatwave official.
To be classified as a heatwave, the temperature must be over 25 degrees for five consecutive days, with three of them over 30 degrees.
However, the high temperatures are unlikely to break the record set in 1944 in the Gelderland town of Warnsveld when the mercury reached 38.6 degrees, weather forecasters say.
On Thursday it reached 38.2 degrees in Maastricht, but although it will remain hot over the weekend, temperatures are not expected to exceed 37 degrees.
Thursday night’s thunderstorms led to a number of fires around the country. These were mainly in farm houses and buildings following lightening strikes.
Traffic management organisation Rijkswaterstaat says roads will be extra busy over the weekend, with people heading off on holiday and to Utrecht for the start of the Tour de France on Sunday.
Trains around Amsterdam, Rotterdam, The Hague and Utrecht are also likely to be packed because Dutch railway company NS has further reduced services, worried that tracks may buckle in the heat.
More thunderstorms are forecast for Friday and Saturday. From Sunday temperatures will be between 25 and 27 degrees with a chance of showers, according to the KNMI weather centre.
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