The main fire in Gironde, home to Bordeaux, was “extremely intense and unpredictable, advancing erratically toward the Bordeaux metropolitan area”, warned Interior Minister Laurent Nunez.
Weather forecasters warn another heatwave could hit France from Tuesday, with temperatures reaching 40C.
King Felipe VI said the wildfires had caused “incalculable” damage to Spain’s natural heritage.
Around 75,000 residents have been evacuated from the Madrid region, Avila, Toledo and Valencia.
One person was killed on Saturday in a separate fire near Valencia, while two firefighters were killed near Bordeaux on Tuesday.
Meanwhile in Italy, coastguards evacuated over 400 tourists by sea near Peschici due to spreading blazes.
