The fires, fanned by scorching heat and strong winds, have spread across 19,300 hectares (about 75 sq miles) in the countryside surrounding Bordeaux since July 12, with a total of 34,000 people forced to evacuate their homes.

About 2,000 firefighters, supported by eight water-bomber aircraft, were battling the blazes.

“Despite attacks from the ground and from the air, the situation has still not stabilised,” the state prefecture said in a statement, adding that there had been no reports of death or injury.

The temperature in Bordeaux was 25 Celsius at midday, with rain expected in the evening.

The Bordeaux Public Prosecutor said in a statement that a man was in police custody in connection with a probe into the Landiras fire, where 12,800 hectares have been burnt.

The region is home to famous vineyards and chateaux but there have been so far no reports of specific damage to the vines.

A second blaze, that has already burnt 6,500 hectares, is raging along the Atlantic Coast close to the Dune du Pilat – the tallest sand dune in Europe – in the Arcachon Bay area, above which heavy clouds of smoke rose into the sky.

As wildfires raged across parched southern France, Spain and elsewhere, Britain was forecast to see temperatures hit 40C (104F) for the first time on Tuesday after logging its warmest night on record.

(Reporting by Dominique Vidalon; Editing by Nick Macfie)