Two forest fires sweeping Spain's eastern Valencia region that have forced 3,000 people to evacuate their homes showed no sign of abating on Sunday, authorities said.

Despite more favourable weather conditions of "lower temperatures, increased humidity and an easterly wind", coming from the Mediterranean, the fires "continue to advance", said authorities.

"Tens of thousands of hectares" had been burned, authorities said, while the Spanish press gave the figure as between 30,000 and 45,000 hectares (74,000 acres and 111,200 acres), making it the biggest fire in the region in the last 20 years.

Some 1,800 firemen, 47 planes and helicopters were mobilised on Sunday to keep it from spreading into residential areas.

A total of 3,000 people were evacuated from local hamlets as well as the staff of a local power plant since the first fire was sparked Thursday though "most were able to return to their homes on Sunday," authorities said.

A dozen roads were also cordoned off.

The first fire in Cortes de Palla in Valencia was sparked during work to fit solar panels on homes in the area.

Two people were arrested and placed under judicial supervision, said a spokesman for the prefecture.

A second fire broke out in Andilla on Saturday.

Summer temperatures nearing 40 degrees Celsius (104 degrees Fahrenheit) following the driest winter in 70 years have fanned the flames.

Also on Saturday about 40 fire trucks battled another blaze in Prats del Rei in the northeastern Barcelona region.