Much of west­ern Eu­rope baked un­der a “heat dome” Wednes­day as tem­per­a­tures soared to­ward 40 de­grees Cel­sius (104 Fahren­heit) in places, and weath­er agen­cies warned that the ex­treme con­di­tions could en­dan­ger lives across coun­tries, many of which have lim­it­ed air con­di­tion­ing.

France record­ed its hottest-ever day for the sec­ond day run­ning. The Me­teo France weath­er agency said the coun­try’s na­tion­al ther­mal in­di­ca­tor — an av­er­age of tem­per­a­tures mea­sured at 30 weath­er sta­tions — hit a new record of 30 C (86 F), the lat­est in a se­ries of nev­er-be­fore-reg­is­tered highs. The mer­cury sur­passed 40 C (104 F) in some lo­ca­tions, in­clud­ing in Paris.

The French weath­er agency put three-quar­ters of the coun­try un­der a red alert for ex­treme heat start­ing at mid­day Thurs­day un­til the same time Fri­day. The warn­ing en­com­passed tens of mil­lions of peo­ple. In the usu­al­ly tem­per­ate Brit­tany re­gion of north­west France, a heat-re­lat­ed equip­ment fail­ure knocked out pow­er to tens of thou­sands of house­holds that had to en­dure with­out elec­tric fans.