By Sunday afternoon, the fire had taken two different directions, burning more than 1,700 hectares (4,200 acres) as it continued advancing, the provincial government said in a series of tweets. Nine helicopters and two planes were aiding at least 600 people including firefighters and army emergency personnel who were working in shifts to tackle the blaze.
Officials described the fire as having "great potential" to spread. The island was experiencing temperatures close to 40 C (104 F), humidity levels below 30% and strong winds, which usually provide what experts call the "perfect storm" for virulent wildfires.
"The environmental damage has already been done," said Ángel Víctor Torres, the region's president, in comments carried by the private Europa Press news agency. "We are facing a complicated situation in which the security of people is the priority now," the official added.
Evacuations extended to at least 40 towns in the vicinity of Valleseco. At least 1,500 hectares (3,700 acres) of field and low forest burned in the same area last week. Wildfires are common in southern Europe during the hot, dry summer months. Nearly half of Spain's provinces were on alert Sunday for a high risk of fires, according to the country's weather agency AEMET.