The mayor of Bordeaux has said he is bracing for “all eventualities”, as one of multiple wildfires burning in France is now 15km (nine miles) from the south-western city.
“We are preparing to accommodate a large number of people should further evacuations be ordered,” said Thomas Cazenave.
President Emmanuel Macron, visiting the fire-ravaged area in the Gironde region, said the country was facing a “completely unprecedented wildfire” – the “toughest since World War Two”.
Some 220,000 people have been evacuated in France and more than 100,000 in Spain, where fires are burning “uncontrolled” west of Madrid.
Another intense heatwave on Tuesday could further hamper firefighting efforts.
Macron said a smaller fire in the Landes region had been contained, but the fight continued in neighbouring Gironde.
While firefighters had made progress on Monday, improving the situation compared to 24 hours before, he warned that “temperatures are set to rise again, the wind is still present, and therefore we must remain humble”.
Earlier, Interior Minister Laurent Nuñez had said the fire “has a life of its own”.
Jerome Steffe, the mayor of Cestas, a town south of Bordeaux, told the BBC this “will be the fire of the century”.
He described how 17,000 residents were evacuated from his town during the night when the fire swelled two days ago. So far, he said, the region has seen 42,000 hectares (103,000 acres) of land burned and 240 houses destroyed.
“In my city the situation is really catastrophic,” he added.
And although the fire is no longer moving as quickly, he said his teams have “won only a small battle” and emphasised that the risk remains from flying embers or a sudden change in wind direction.
“We put all our energy into creating protective firebreaks,” he explained, but admitted “we are all scared in front of this situation.”
French Prime Minister Sébastien Lecornu warned the country “is going through an unprecedented fire season”, with 116,085 hectares (286,852 acres) burned and 13,566 fire starts recorded since January.
The minister revealed in a post on X that nine out of 10 fires “are human-caused and most arise from carelessness: a cigarette butt, a barbecue, work carried out without precaution”.
But he also said that not all these fires are accidents and some are deliberately set, adding that since 6 July, 162 arrests have taken place.
Wildfires are also burning in several other French regions, including Var and Landes, and also in Haute-Corse on the island of Corsica.
Meanwhile, neighbouring Spain on Monday entered its fifth day of a national emergency because of raging wildfires west of the capital Madrid.
BBC Verify has been analysing satellite imagery showing the spread of the wildfire west of Madrid, which has now affected more than 27,000 hectares.
Satellite images, captured on 24 and 26 July, show how the fire spread over two days after several blazes in the Almorox, Villa del Prado and San Martín de Valdeiglesias areas merged into one large fire.
