Improperly stored chicken manure that spontaneously combusted during a heat wave is reportedly the likely cause of an out-of-control wildfire that has burned more than 13,000 acres in Spain.

At least 53 residents of Catalonia, in the northeastern part of the country, were evacuated and the land was littered with hundreds of dead sheep and horses caught in the path of the blaze, USA Today reported. More than 500 firefighters have been working to quell the flames.

ARIZONA WILDFIRE FORCES 700 EVACUATIONS; WINDS CAUSING WIDESPREAD FLAMES

Spontaneous combustion can happen when a material reaches a high enough temperature to ignite, according to Wired.

The regional interior director called it the region’s worst wildfire in 20 years. “"Let us be very aware that any irresponsibility can end up being a catastrophe," he wrote in a tweet. ”Maximum precaution," USA Today reported.

The Catalan regional government said Friday that progress had been made but the fire was not yet extinguished, according to Aljezeera.