Tuesday will enter the record books as the warmest September 15 and warmest Prinsjesdag on record, weather forecasters say.

Weather station Voorschoten/Valkenburg, the measuring point closest to The Hague, clocked up in unprecedented 30.03 Celsius, weather bureau Weeronline said.

Budget day or Prinsjesdag is a moveable feast, celebrated on the third Tuesday in September so dates vary. The last budget day record dates from September 19 1961 when the temperature in The Hague reached 28.7 Celsius

It is also officially the hottest  September 15 on record, with 30.5 degrees measured at the De Bilt weather station, making it an official tropical day.

The health institute RIVM issued a smog warning for large parts of the country, particularly in the afternoon. Intense sunshine and little wind concentrates harmful pollution and people with asthma and other respiratory problems are better off staying indoors, the RIVM said.

Wednesday and Thursday will still be warm and sunny with top temperatures of 29 and 24 degrees respectively. Temperatures will remain in the low 20s until Monday when some showers are expected, Weerplaza said, and temperatures will dip slightly under 20 degrees as the week progresses.