French firefighters are battling a huge blaze in a forest just south of Paris as a devastating heatwave extends its deadly sweep across Europe.

More than 3 square miles (800 hectares) of the Fontainebleau forest have been burned, reported CNN affiliate BFMTV on Monday, and fire-fighting aircraft have been scooping up water from the River Seine as part of efforts to get the fire under control.

French Interior Minister Laurent Nuñez told reporters police are investigating whether the fire was started deliberately. Wildfires had also broken out in other parts of the country, Nuñez said in a post on X on Sunday.

Wildfires are not unusual in Europe, but the climate crisis is driving hotter, drier weather, which is setting the stage for fiercer fire seasons. They are also happening earlier in the year and are of growing intensity.

In much of France and Spain, an exceptionally wet winter left a lot of vegetation that quickly turned to tinder as three successive heatwaves sent temperatures into the high-30s Celsius.