The fires have torn through a region already battered by a blisteringly hot and dry summer.
Crews were seeking to capitalise on more favourable weather before a new wave of higher temperatures settled in from Wednesday.
In the Bordeaux region of France, firefighters contained the forest blaze overnight, while in Spain, authorities allowed people from nine out of 11 towns in the central Toledo province to return to their homes.
However, fires still raged out of control in Madrid and nearby provinces, prompting heightened vigilance.
One Spanish evacuee described a "red hell" of fire, portraying intense scenes as residents fled with little more than clothes on their backs.
Europe, the world's fastest warming continent, has endured record-breaking heatwaves in 2026.
Scientists say human-driven climate change is intensifying the heat and drought that allow wildfires to spread faster, burn longer and become more destructive.
"The situation we are dealing with today is the most severe we have ever recorded, the toughest since the Second World War," French President Emmanuel Macron said.
"We are facing a completely unprecedented wildfire," he told emergency workers in Bordeaux late on Monday.
Wildfires in France have now burned more area than at the same time in any year since 2006.
Despite progress in the firefighting effort, the situation remained difficult, said Nathalie Delattre, senator for Gironde, which covers the city of Bordeaux.
"Everything will depend on how the firefighters on the ground get on," she told BFM TV on Tuesday.
Campsites and tourist residences at Lacanau, by the Atlantic coast near Bordeaux, were being evacuated on Tuesday, the Lacanau local administration said on its Facebook page.
Spain is bracing for its fourth heatwave of the summer from Wednesday with the risk of fire expected to reach extreme levels due to high temperatures, southerly winds and low humidity.
Firefighters are still battling fires in the region of Madrid and neighbouring provinces of Avila and Toledo.
Conditions during the night in Madrid enabled active fire fronts to be tackled effectively, helping to reduce the threat, though the fires are not yet under control, the Spanish government said.
As of Tuesday, Spain had more than 73,000 evacuees and roughly 66,000 people under confinement.
According to the Reuters Climate Monitor, temperatures in Bordeaux were forecast to hit 33C on Tuesday, 7.1C higher than the daily average in 1961 to 1990, while the Madrid region's 37C would be 5.5C above average.
This week's heatwave is expected to build quickly and peak on Wednesday.
Meteo France also expected the heat to peak on Wednesday, when temperatures in Paris could hit 38C, but said the duration of the heatwave "will be determined in the coming days".
The UK Met Office said it was forecasting "an increasingly warm, but relatively short-lived, spell of hot weather".
For those caught in the fire's path, escape often came down to grabbing relatives and pets, and leaving everything else behind.
Sitting on a camp bed at a French evacuation centre and stroking her cat, consultant Sylvie Michel, 63, praised authorities for providing her and her pets with everything they need.
"In France we tend to be very critically-minded, to put it mildly. And honestly, hats-off to everyone involved," she said.
Spanish evacuee Jose Miguel Encinas, 53, in La Vall d'Uixo in eastern Spain recalled scenes of "total chaos".
"It was like in the movies where hell cracked the ground open, and you see the red hell."
