The fire in the Sierra de Culebra in Zamora province has already scorched 31.000 hectares (1.770 acres).
State-run news agency Efe reported it was the largest on record since a fire in southwestern Huelva province in 2004 gutted almost 30.000 hectares (167.000 acres) of surrounding area.
Several of the fires are still burning, and firefighters are working to extinguish the blaze, which has laid waste to more than 74.000 acres.
A drop in temperatures enabled around 650 Firemen aided by water cannons to set up a perimeter around the fire, which engulfed the city on Wednesday.
People from 18 villages needed to be evacuated during the past week.
Elsewhere, 900 people have been evacuated from 13 villages in Navarre in the northern region, where two forest fires have been burning raging.
Spain, Germany battle forest fires amid uncommon heat wave