A forecast of an incoming heat wave across France and Spain this week is threatening to hamper firefighting efforts as some of Europe's worst wildfires in decades rage on.

France's weather service forecast temperatures of up to 40 degree Celsius from Tuesday, while Spain's AEMET warned of a new heat wave from Wednesday till the end of the week, with highs of 42 degree Celsius in the northeast and 39 degrees Celsius in central regions.

Authorities said soaring temperatures, dry winds and low humidity would push wildfire danger to "extreme" levels, even as forests turned tinder-dry by successive heat waves this year.

The return of searing temperatures, from Tuesday in France and from Wednesday in Spain, threaten to complicate fire-fighting efforts [FILE: July 23, 2026]Image: Julien De Rosa/AFP

Thousands of firefighters and water-dropping aircraft raced to contain the blazes before temperatures rise further.