LONDON — Never in recorded history has Paris been hotter than it was Thursday (July 25).

The same was true of Belgium, Germany and the Netherlands, as temperatures rose and records tumbled one by one across Western Europe, scorching the continent and sending residents scrambling to seek relief from a dangerous heat wave.

In Paris, the temperature soared to 42.6 degrees Celsius (108.6 Fahrenheit), breaking a record set in 1947, 40.4 degrees Celsius, according to the French national weather service, which said the temperatures could rise further. Some 20 million people in northern France were expected to be affected by the heat.

In the Netherlands, temperatures topped 40 degrees Celsius (104 Fahrenheit), shattering the record high set only a day earlier, the Royal Netherlands Meteorological Institute said. In Germany, the northwestern town of Lingen hit 41.5 Celsius (106.7 Fahrenheit).

And for the second time this week, Belgium measured its hottest day, with a temperature of 40.6 Celsius in Kleine Brogel (105 Fahrenheit) on Thursday, passing the mark set a day earlier, 40.2 Celsius. Authorities issued a code red alert for the first time since the weather warning system was put in place 20 years ago.

“It’s really shocking to have this heat in Brussels,” said Ms Francesca Van Daele, a student of political science at the Free University of Brussels-VUB. “Our urban planning is not really made for heat waves like this.”

The hottest summers in Europe in the past 500 years have all come in the past 17 years, scientists say. Several heat waves have been linked to human-caused climate change. In the years ahead, they say, many more are likely to scorch temperate zones like northern Europe.

Early Thursday, the No. 1 trending term on Twitter in Britain was #hottestdayoftheyear. The national weather service, the Met Office, had warned that temperatures were expected to break the national record, 38.5 degrees Celsius (101.3 Fahrenheit). By 4pm (11pm Singapore) , Cambridge, England, had measured 38.1 degrees Celsius (100.5 Fahrenheit), the hottest day recorded in July in Britain and the second hottest in general, according to the weather service.

“This is only the second time temperatures over 100 Fahrenheit have been recorded in the UK,” the Met Office tweeted.

Ms Nicky Maxey, a spokeswoman for the weather service, said in an email, “Heat waves are extreme weather events, but research shows that with climate change, they are likely to become more common, perhaps occurring as regularly as every other year.”

She said that a Met Office study into the heat wave that Britain experienced last summer showed it was 30 times more likely for a heat wave to occur now than in 1750 “because of the higher concentration of carbon dioxide in the atmosphere.”

The Met Office placed five of England’s nine regions, including London, on a rare Level 3 heat health watch — one short of a national emergency. In a Twitter post Thursday, London’s ambulance service advised Britons to stay hydrated, avoid prolonged exposure to the sun, wear sunscreen and avoid travelling by train if they feel unwell.

Mr Owen Landeg, chief environmental public health scientist at Public Health England, warned that extremely high temperatures were most likely to affect older people, those with underlying health conditions and very young children.

“The extreme heat means that our bodies, especially our hearts and lungs, have to work harder to maintain a normal temperature,” he said Wednesday in a statement. “This is why our advice focuses on reminding people to keep an eye on those who are most at risk.”

In Germany, officials expected higher temperatures in the west Thursday, and all but the northeastern coastal region was under a heat warning, with officials urging people to drink enough fluids and avoid going outdoors in the afternoon hours.

The famed Wagner opera festival was set to open as scheduled Thursday in the southern city of Bayreuth, where temperatures were expected to reach 34 degrees Celsius (93.2). But it will be even hotter inside the 19th-century opera house, where air conditioning was rejected over fears that it would negatively alter the acoustics and endanger the singers’ voices. Chancellor Angela Merkel was expected to be in the crowd for the opening performance of “Tannhäuser,” which is more than four hours long.

In Spain, the forecast was for temperatures to fall across the country Thursday night, with rain in the northwest. The same was expected in Portugal, where no major fires were burning.

In Austria, the national railway service began painting stretches of track in white, in hopes of preventing them from getting so hot that they bend. Similar projects were taking place in parts of Germany and Switzerland.

A Eurostar train broke down Wednesday morning in Tubize, Belgium, en route to London from Brussels. Despite the heat, passengers were not allowed to open windows or leave the train for three hours because of safety concerns.

“Everything was suddenly down. No air conditioning, no electricity,” said Mr Paul De Grauwe, a Belgian economist who was on the train. “I have never been so hot in my life.”

Such high temperatures are rare in Belgium but are becoming more typical, experts say. In the 1990s and 2000s, heat waves of this magnitude occurred once every three or four years, but Belgium has experienced two heat waves in the past two months alone.

On Thursday in France, when the mercury rose to 41 degrees Celsius (105.8 degrees Fahrenheit) at 1.42 pm (7.42pm Singapore time) local time , Mr Olivier Proust, a forecaster for the French national weather service, said, “Such a situation is historic because all over France heat records are broken.”

By noon in Paris, the Trocadero fountains near the Eiffel Tower had morphed into public swimming pools as people were jumping under the water jets, seeking relief from a heatwave that started Monday.

“It’s too hot in my apartment; I can’t take it anymore,” said Ms Nadia Zouaoui, a 23-year-old woman who was bathing with her two children in the fountains. “My kids really need to freshen, otherwise it’s unbearable for them.”

French authorities had issued hundreds of warnings to avoid the devastating death toll the country suffered during the 2003 heat wave, which contributed to almost 15,000 deaths.

“Everyone is at risk with these kinds of temperature,” Health Minister Aghes Buzyn told reporters Wednesday.

Volunteers could be seen on the streets of Paris on Thursday handing out water bottles, and City Hall introduced restrictions on car use because of the high levels of air pollution.

The weather has led to some odd sights in London.

After a sweating man in a half-unbuttoned, pink-striped shirt opened a window in a crowded subway car on Wednesday, sweltering commuters made rare eye contact, trading looks of approval and relief.

And on the outskirts of Hampstead Heath, a vast park in northwestern London, hundreds of people flocked to a greenish pond to seek relief Thursday, sunbathing, picnicking, reading or listening to music. Dozens insisted on splashing in the pond, even after an announcement that broken bottles posed a danger to swimmers.

“On days like today, I can almost excuse climate change,” Mr Hylston Chambers, 52, said with a smile.

Mr Charlie Edmonds, a 22-year-old freelance choreographer who was spending the day at the pond on the edge of Hampstead Heath, said, “I’m sweating like crazy, but I’m pleased it’s hot in England,” he said.

The Met Office predicted a break in the heat wave: Temperatures are expected to cool Friday, said Mr Frank Saunders, chief meteorologist at the Met Office.

“Conditions will feel much more comfortable for western parts of the UK by the time we get to Friday,” he said.

The forecast even called for thunderstorms Friday. And about 6.30 pm Thursday local time, rain began falling in London. THE NEW YORK TIMES