In France, hundreds of firefighters, supported by six water-bomber aircraft, battled two fires in the southwest, prompting the evacuation of thousands of campers during the long summer holidays, Gironde prefect Fabienne Buccio said.
In Santiago de Guarda in the central Portuguese district of Leiria, Albertina Francisco struggled to hold back tears as a cloud of black smoke billowed over the tiny village.
"It was very hard," said Francisco, 42, who was helping her sick sister evacuate.
"Nobody helped - the firefighters and the (water-bomber) aircraft only got here now. The state must do more to help us."
In Leiria, where more than 3000 hectares have burned so far, authorities blocked major motorways and side streets as strong winds made it harder for firefighters to fight the flames.
Portugal's most important highway, connecting its capital Lisbon to second-city Porto, was blocked due to another fire further north.
Nearly 900 firefighters were combating three active blazes in Leiria alone, while in the whole of mainland Portugal there were 2841 firefighters on the ground and 860 vehicles.
In Portugal's southern Algarve region, popular with tourists, a fire broke out in the city of Faro and spread to the Quinta do Lago luxury resort.
Videos shared online showed flames edging close to villas, burning palm trees and parts of golf courses.
About half of drought-hit Portugal will remain on red alert for extreme heat conditions on Thursday, with the highest temperatures expected in the Santarem and Castelo Branco districts, the IPMA weather institute said.
Wednesday's highest temperature was registered in the central town of Lousa at 46.3C, one degree below a 2003 record.
At least 135 people have suffered mainly minor injuries since fires flared in Portugal last week, and about 800 people have been evacuated from their homes, according to the Civil Protection Authority.
Almost 3000 hectares have burned so far in France's Gironde region, prefect Buccio told BFM TV.
The biggest of the two fires is around the town of Landiras, south of Bordeaux, where roads have been closed and 500 residents evacuated.
The other is along the Atlantic coast, close to the iconic Dune du Pilat - the tallest sand dune in Europe - located in the Arcachon Bay area.
That fire led to the evacuation of 6000 people from five surrounding campsites.
On the eve of the annual Bastille Day celebrations, the Gironde prefecture has forbidden all fireworks until Monday in towns and villages in close proximity to forests.
The World Meteorological Organisation warned on Tuesday the heatwave was spreading and intensifying in large parts of Europe.
With human-caused climate change triggering droughts, the number of extreme fires is expected to increase 30 per cent within the next 28 years, according to a February 2022 UN report.
Searing temperatures also swept across China's vast Yangtze River basin on Wednesday; firefighters tackled a forest fire near the tourist town of Datca in Turkey; and power demand in Texas hit an all-time high as consumers cranked up their air conditioners to escape the heat.
In Spain's western region of Extremadura, bordering Portugal, firefighters battled a blaze that swept into Salamanca province in the region of Castile and Leon, burning more than 4000 hectares.
Parts of the Extremadura, Andalusia and Galicia regions were on red alert for extreme heat, Spain's AEMET meteorology service said, adding the country's highest temperature on Wednesday stood at 45.6C in Huelva province.
