Tour de France cyclists competed in scorching temperatures and a French nuclear power plant prepared to shut down today as western Europe baked in a new heatwave already breaking longstanding records.

Overheating tourists in Paris and Berlin plunged into fountains and ornamental ponds to keep cool while zoo keepers in the Netherlands handed out food caked in ice to look after thirsty animals.

The southwestern French city of Bordeaux saw its highest ever temperature since records began of 41.2 degrees Celsius, beating the previous high of 40.7C registered in August 2003, weather service Météo-France said.

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

The same day could also mark the all-time record temperature for the French capital Paris, whose current record has stood at 40.4 degrees Celsius for over seventy years.

Météo-France currently has a record 81 of the country's 96 mainland departments on an orange weather alert, meaning citizens should be highly vigilant.

Nuclear shutdown

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 this evening and number 1 on Wednesday, with both due to stay shut until 30 July.

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.

The government outlawed animal transportation "for economic reasons" between 1pm and 6pm in areas affected by heat alerts.

Unlike the scorching heatwave at the end of June, the current blast of hot air is most severe in parts of northern Europe completely unaccustomed to such temperatures.

'Extremely hazardous'

In Britain - where temperatures could exceed the all-time record of 38.5 degrees Celsius 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.

Berlin, Germany: People walk near the Reichstag during hot weather

In Bordeaux, a host of charities accused the local prefecture of "putting more than 300 people out on the street" after evicting migrants from squats in May and July.

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

In the Vosges mountains of eastern France, farmers have been forced to let their cattle graze pastures on what are ski slopes in winter in order to feed them.

'Irreversible breakdown'

The new heatwave also amplified concerns that human activity is heating the planet at a dangerous rate.

The June 26-28 heatwave in France was four degrees Celsius 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, told MPs at French parliament of dire consequences if "business as usual" continued until 2030.

"We will likely be in a position where we may pass a number of tipping points and we will be unable to undo the irreversible breakdown," she said.

Greta Thunberg