Fans flew off store shelves and public fountains offered relief from the heat as temperatures soared in Europe on Monday, with officials urging vigilance ahead of even hotter conditions forecast later in the week.
Meteorologists blamed a blast of torrid air from the Sahara for the unusually early summer heatwave, which could send thermometers up to 40 degrees Celsius (104 Fahrenheit) across large swathes of the continent.
Authorities have issued warnings against dehydration and heatstroke, in particular for children and the elderly, and hospitals have been placed on high alert.
"I'm worried about people who are downplaying this, who are continuing to exercise as usual or stay out in the sun," French Health Minister Agnes Buzyn said.
"This affects all of us, nobody is a superman when it comes to dealing with the extreme heat we're going to see on Thursday and Friday," she told a press conference.
"It's unprecedented because it's hitting so early in June, we haven't seen this since 1947," said Emmanuel Demael, a forecaster at the Meteo-France weather agency.
He expects records will be set for the month, "and in some places records for all months combined."
In Paris, officials pledged to open "cool rooms" inside public buildings, set up temporary water fountains, and leave the city's parks unlocked at night.
City workers also plan to distribute water to the homeless and install fans in schools and nurseries.
But fans were in short supply after weather reports prompted a rush on stores over the weekend, and France's electric grid operator RTE is expecting a surge in demand as air-conditioning is turned up to maximum.
French retailer Boulanger said sales of "air treatment" equipment had jumped 400 percent from normal levels in recent days.
- Records in view -
Spain's AEMET weather agency warned of an "extreme risk" of forest fires in areas including Aragon, Navarre and Extremadura, with temperatures that could exceed 42 degrees in the Ebro valley in the northeast.
In Germany, forecasters said the June record of 38.2 degrees for Frankfurt in 1947 was likely to come under threat, with little prospect of storms to cool things down.
"It could get up to 39 degrees, some places could even crack the 40 degree mark," said Sabine Krueger of the German weather service, with the southwest due to be the hottest.
Even Scandinavian countries aren't being spared, with parts of southern Denmark and Sweden likely to reach 30 degrees starting Tuesday.
The temperatures will be most intense from Thursday, forecasters say, and high humidity is likely to make conditions even more difficult, especially at night.
France's Labour Minister Muriel Penicaud urged businesses to "adapt their hours and equipment" to help employees cope.
Meteorologists have said such heatwaves are likely to be more frequent, even if countries succeed in their commitments to limit global temperature increases as part of the 2015 Paris climate accord.
The deal aims to contain increases to 1.5 degrees Celsius (2.6 Fahrenheit), committing nations to reduce emissions to this end.
The European Union pledged to cut carbon emissions 40 percent below 1990 levels by 2030.