Forecasters predicted new temperatures highs in a string of countries, including Belgium, Luxembourg and the Netherlands, where the mercury is set to reach 40 degrees Celsius (104 Fahrenheit) for the first time on Thursday.

The same day could also see the all-time record temperature for the French capital Paris -- 40.4 degrees Celsius (104.7 degrees Fahrenheit) in 1947 -- beaten.

And as the Tour de France reached its final week in the southeast of the country, ice foot baths and extra water points were on hand to avoid dehydration.

"In the third week of the Tour de France, I think heat like this could make the difference," said Davide Bramati, head of sport for team Deceuninck, whose cyclist Julian Alaphilippe is currently leading the world-famous race.

French energy company EDF said it would temporarily shut down the two reactors at its Golftech nuclear power plant this week in the southern Tarn-et-Garonne department, in a bid to limit the heating of water used to keep reactors cool.

Reactor number 2 will shut down on Tuesday evening and number 1 on Wednesday, with both due to stay shut until July 30.

France is gearing up for a surge in electricity use this week, but the national electricity board said Monday that there will be enough supplies.

- 'Extremely hazardous' -

Authorities around Europe also issued health warnings, encouraging older or vulnerable people to be particularly vigilant.

In Britain -- where temperatures could exceee the all-time record of 38.5 degrees Celsius (101 Fahrenheit) on Thursday -- asthma sufferers were warned of a "toxic cocktail" of hot, humid weather and rising pollution levels.

This "could be extremely hazardous for the 5.4 million people in the UK with asthma, triggering deadly asthma attacks," said Andy Whittamore, clinical leader at charity Asthma UK.

In the Netherlands -- where most of the country was hit by a "code orange" alert Tuesday -- the government activated its "national heat plan", issuing advice for hospitals, retirement homes and even obese people.

Animals were also a cause for concern.

In France, the government banned animal transportation "for economic reasons" between 1:00 pm and 6:00 pm in areas affected by "orange" and "red" heat alerts.

Paris and the eastern city of Lyon have also banned more heavily polluting vehicles from the city centre in a bid to keep the air clean.

The heatwave has also caused water shortages in dozens of regions across France, with a drought raising concerns for farmers producing a host of crops from potatoes to grapes.

The new heatwave in northern Europe follows a three-day temperature peak from June 26-28 in France, which was four degrees Celsius (7.2 Farenheit) hotter than an equally rare June heatwave would have been in 1900, the World Weather Attribution (WWA) team said this month.

One study by the Swiss Federal Institute of Technology said the deadly, weeks-long heatwave across northern Europe in 2018 would have been statistically impossible without climate change.

Swedish teenage climate activist Greta Thunberg, who has highlighted the problem of global warming through school strikes, spoke at the French parliament on Tuesday.

Some right-wing MPs have said her visit is needless, with Julien Aubert of the Republicans describing her as a "prophetess in shorts, a Nobel Prize for Fear" in comments denounced by green activists.