Storms born of flame: What ‘fire clouds’ are, and why Europe's worst wildfires in decades may burn for weeks

Pyrocumulonimbus, or 'fire cloud', formed over Gironde for the first recorded time in France, generating lightning and erratic winds that spread the fire.

Wildfires in France and Spain have forced over 300,000 people from their homes, with the Gironde blaze burning 420 sq km, about four times the size of Paris.

Spain's Ávila fire, at 500 sq km, is the largest in recorded Spanish history, a government spokesperson said.

A fresh heatwave arriving in France and Spain threatens to worsen the fires, which may burn for weeks according to officials.

French President Emmanuel Macron called the situation France's worst fire crisis since World War II, as the fire damaged or destroyed over 240 homes and injured 80 firefighters.