Two Greek firefighting helicopters collided in mid-air on Sunday as they were battling a wind-driven wildfire west of Athens, sending one aircraft crashing to the ground, footage showed.

The four crew members were recovered, the Greek fire department said. Two were recovered safely while the other two were unconscious. The collision laid bare the danger at the most volatile front of Europe’s wildfire emergency. Strong winds drove flames deeper into the region of the Greek capital and forced fresh evacuations, France guarded a still-burning scar four times the size of Paris, while Spain’s major fires stopped advancing.

The aircraft were Bell helicopters operating over the Psatha area west of Athens, each with a two-person crew. Two of those aboard were Greek and two were foreign nationals, but authorities did not identify their countries. Flames spread rapidly through western Attica, threatening communities and an industrial district outside Megara as violent gusts prevented firefighting aircraft from collecting water from the sea. The advance carried grim resonance in a region where the 2018 Mati wildfire killed 104 people, Europe’s deadliest blaze this century.