There will be moderate to heavy smog across much of the Netherlands on Friday, public health institute RIVM warned on Thursday.

Smog is formed by a combination of sunlight, air pollution from car exhausts and little wind. It is hazardous to human health.

Consequently, the RIVM is advising people not to undertake heavy physical activity on Friday. People with breathing problems, such as asthma sufferers, and children should stay indoors and keep their windows closed.

The worst fog is expected in eastern parts of the country.

Weather forecasters already warned temperatures on Friday could reach as high as 37 degrees Celsius.

Motorists

Anyone leaving a child or dog in their parked car must ensure shade by covering the side windows, and leave sufficient water, motoring organisation ANWB says.

There were several incidents during last week’s heatwave of fire brigades smashing open cars to rescue dogs.

Warmest day

The warmest day ever recorded in the Netherlands was August 23 1944 in Warnsveld in Gelderland when the temperature reached 38.6 degrees Celsius.

Weather forecasters are now anticipating a similar record on Friday. ‘The absence of a sea wind will help,’ Meteoconsult told website nu.nl. ‘But other pieces of the puzzle need to fall in place, such as low pressure from the south not reaching the Netherlands.’