The fire, which has been burning in the city Navalcruz since Saturday morning, has been fed by winds of up to 70 kilometers an hour (54 miles per hour) across the Iberian peninsula.
It now has a perimeter of more than 40 kilometers and may already have burned more than 5,000 hectares (12,350 acres), said Jose Angel Arranz, forestry director of the Castilla y Leon region, sources reported.
The authorities have already evacuated at least 600 people from five towns in the Avila district, near the Sierra de Gredos mountain range, and more than 500 firefighters are tackling the blaze with the help of specialized aircraft.
Around 80 kilometers to the south meanwhile, another fire, near El Raso, was still active. Like the one in Navalcruz, it is rated two on a three-point scale of seriousness.
The emergency services backed by 12 firefighting aircraft have also been fighting a blaze in Azuebar, eastern Spain, since Saturday, which has burned more than 500 hectares, the regional government in Valencia reported.
The blaze is a threatening part of the Sierra de Espadan Natural Park.
HJ/PR