Firefighters evacuated about 1,000 people from the town of Hoyos in the early hours of Saturday, a day after another 1,400 people were ordered to leave their homes and campsites in two other nearby towns.
"The wind fanned the flames and caused the fire to spread, forcing the evacuation of Hoyos due to the proximity of the blaze and especially the smoke," local Red Cross official José López Santana told Spanish public radio.
The blaze, which broke out on Thursday in the Sierra de Gata mountain range amid scorching temperatures, has burned more than 5,000 hectares (12,400 acres) of land, the government of the Extremadura region said in a statement.
"For families it is very hard not being able to remain at home but saving lives must be our top priority," the head of the regional government, Guillermo Fernandez Vara, told reporters.
The cause of the fire was still undetermined but "everything seems to indicate" that arson was to blame, he added.
"When a fire is concentrated in a very specific area it is because the hand of man must have played some kind of a role, because it is not hotter and drier in the Sierra de Gata than in the rest of Extremadura," he said.
Six roads in the Sierra de Gata mountain range were closed because of the fire.
Winds were expected to slow throughout the day, helping firefighters to bring the blaze under control.
Firefighters were battling four other wildfires burning in the southeastern region of Murcia.
The fires, which were all started on Thursday by lightning strikes, have so far burned more than 700 hectares of land, local officials said.
The risk of wildfires was high in western Spain and large parts of the country's Mediterranean coast on Saturday because of high temperatures and low air humidity levels, according to national weather agency AEMET.
Wildfires have destroyed more than 54,000 hectares of agricultural and forest land in Spain this year, exceeding the amount burned during the last two years combined, according to the agriculture ministry.
Most of the wildfires happened in July, which was the country's hottest month on record.
The average temperature in Spain last month was 26.5 degrees Celsius (79.7 Fahrenheit), the agency said Wednesday.
August 2003 had previously been the hottest month on record with an average temperature of 26.2 degrees Celsius.