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.

That has led to a spike in the number of larger fires, according to data from the European Forest Fire Information System (EFFIS).

Extreme heat is also driving excess deaths. In France, more than 2,000 deaths during the last week of June were attributed to the heat. France saw its hottest day ever on June 24.

Deaths rose 29% in the last week of June compared to the week before, according to French Health Minister Stéphanie Rist, who noted a “clear increase” in deaths among those aged over 45.

And this trend is likely to continue in the coming years as Europe is the world’s fastest-warming continent, with temperatures increasing more than twice as fast as the global average, according to the EU’s Copernicus Climate Change Service.

CNN’s Lisa Courbebaisse and Elina Baudier Kim contributed to this report.