French authorities ordered the total evacuation of the Cap Ferret peninsula, a tourism hotspot busy for the summer season, as smoke and flames drew closer to homes.
About 63,000 people were evacuated from the area, many brought to safety by boat, officials said.
Close by, in the town of Biscarrosse, another large fire also forced residents to leave their homes.
"From our home, we had a view of the fires ... We could see the clouds becoming darker and darker," said Yoan Urien, 26, who left late on Thursday after police told everyone in his neighbourhood to leave.
"I was able to find somewhere to take shelter with my pets, but ... it's quite a shock."
A fire that began in Saumos, north of Cap Ferret, is threatening to cut off the only road out of the peninsula and is the largest so far this season in France, Interior Minister Laurent Nunez told local television.
It had torn through 10,000 hectares of land and burned 80 homes, destroying about 50 of them, he said.
In Spain, more than 10,000 people were evacuated from towns in the mountains west of the capital, Madrid, as firefighters sought to prevent three fires in the region and neighbouring Avila province from joining, Interior Minister Fernando Grande-Marlaska said.
The area, where many residents from the capital have second homes, is densely populated.
That played a role in the government decision to declare a national emergency, allowing it to better co-ordinate the response, Grande-Marlaska said, adding that the aggressive nature of the fires and hot, windy weather also prompted the move.
It was the first time such a measure has been taken due to a wildfire.
The last time Spain declared the same level of emergency alert was during a massive nationwide power blackout in 2025.
Spain has also sought assistance from the EU, the Interior Ministry said.
In Navaluenga in Avila province, local residents wearing masks because of the smoke stood watching firefighting helicopters scoop up water from the town's river.
More than 270 emergency personnel and 40 ground units have been deployed in the affected areas, alongside several Military Emergency Unit contingents, Spanish officials said.
It is the second consecutive year that Spain has faced a particularly destructive fire season.
More than 29 major fires have broken out in Spain in 2026, damaging a surface area five times greater than at the same stage in 2025, when a record area was destroyed, Environment Minister Sara Aagesen said in a social media post.
French President Emmanuel Macron said he had asked for firefighting support from the EU to help tackle the Cap Ferret blaze, which has already devastated 8700 hectares.
Several specialist aircraft from other European countries should soon be on their way to help, Macron said on X.
After a short reprieve at the weekend, average temperatures in France are expected to rise sharply again next week, according to Global Forecast System data compiled by LSEG.
