The public health institute RIVM has issued a warning to people in the southern provinces of Gelderland, Overijssel, Noord-Brabant and Limburg, urging them to take proper care of themselves in the heat.

The RIVM says people should be sure to drink enough, wear thin clothes, reduce physical exercise in the afternoon and stay in the shade as much as possible to cope with the high temperatures.

The elderly, the overweight and people in care homes are most vulnerable to the high temperatures and should take extra care, the RIVM said.

The temperature topped 30 degrees in many places on Tuesday and it is expected to be even hotter on Wednesday. Overnight the temperature will drop to no lower than 19 degrees, the KNMI weather bureau said.

The Red Cross is out in force to pass on tips to walkers taking part in the Nijmegen Vierdaagse four day marches. Several dozen competitors have been taken ill because of the weather, the organisers told website Nu.nl.

In 2006 the event was cancelled after two people died of heat stroke.