Temperatures were already set to top 30 degrees Celsius (86 degrees Fahrenheit) on Monday in Paris, but the mercury could soar beyond 40C on Thursday and topple a temperature record dating back to 1947.
The severe heat, which forecasters say will only last a few days but will be exceptionally intense, is expected to affect northern France and parts of Belgium, Luxembourg and the Netherlands.
"It's likely that these three countries see temperatures at or above 40C for the first time," Francois Jobard, a forecaster from the French Meteo France weather office, told AFP.
The new blast of hot air comes less than a month after a heatwave scorched Europe at the end of June, forcing new attention on the issue of climate change.
"The heatwave that is too much," said the headline in the Le Parisien daily on Monday, highlighting that "Act II" of this summer's severe weather would further hurt production of crops from potatoes to grapes.
- 'Historically hot' -
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"Thursday (July 25) will be a potentially historically hot day," added Jobard from Meteo France.
"We are forecasting 41 or 42 degrees in Paris on Thursday and there is the strong chance of beating the record," he added.
The highest ever temperature recorded in Paris was 40.4 degrees Celsius (104.7 degrees Fahrenheit) in 1947. Since records began in 1873, this was the only time a plus-40 temperature was recorded in the French capital, he said.
Other French cities could also see their all time records tumble on Thursday including Reims, Bourges, Lille and Clermont Ferrand, he said.
Britain will also see high temperatures, but will still be significantly cooler than countries on the continent.
Forecasters predict there is a chance the 36.7 degrees Celsius (98.1 degrees Fahrenheit) record high for July -- set on July 1, 2015 at London Heathrow Airport -- could be broken.
Germany was already experiencing several forest fires and drying river beds while farmers fear another bad crop after last year's low yield which was also caused by an unusually hot summer.
The French government has warned that wine production will be down by between six to 13 percent over 2018, notably because of the ongoing heatwave.
Huge wildfires that have ravaged the mountainous Castelo Branco region of central Portugal and left dozens injured have been "90 percent" controlled, firefighters said Monday, but warned that strong winds could cause the flames to spread.
- Global warming? -
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The new heatwave in northern Europe came as the United States also sweltered in extreme hot temperatures.
The New York City Triathlon, which had been scheduled for Sunday, was cancelled for the first time since its founding in 2001.
Scientists are increasingly confident that man-made climate change is driving up the length and intensity of heatwaves -- the period of record-breaking temperatures in June was found to have been between five and 100 times more likely due to global warming.
The three-day temperature peak from June 26-28 in France 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 also said the deadly, weeks-long heatwave across northern Europe in 2018 would have been statistically impossible without climate change.
France saw its highest ever temperature on June 28 -- 46.0 degrees Celsius (114.8 degrees Fahrenheit) in Verargues in the Herault department of southern France.
With the south of the country spared the worst of the current hot blast, this new all-time record is not expected to be challenged for now.