The firefighting effort faced "many difficulties" due to high temperatures and winds of up to 40 kilometres per hour (25 mph), said regional environment minister Juan Carlos Suarez-Quinones.

"We will not allow people to return until safety in their communities is absolutely guaranteed," he told reporters, estimating that about 700 people remained displaced.

Four people, including two firefighters, suffered minor injuries, he added.

The blaze broke out on Sunday near the UNESCO World Heritage Site of Las Medulas, a Roman gold-mining area famed for its striking red landscape in northwestern Spain.

Authorities said that damage to the site will be assessed once the fire is fully under control.

The regional government's tourism department plans a technical evaluation when conditions allow.

UNESCO describes the site as "unquestionably the best preserved and most representative of all the mining areas of the Greco-Roman world in classical times."

Spain has been in the grip of a heatwave for the past week, with temperatures nearing 40 degrees Celsius (104 Fahrenheit) in many areas and fuelling wildfires.

The northwestern Castile and Leon region alone has seen 13 fires in the past three days, according to Suarez-Quinones, who said that some were believed to have been deliberately started.

"Some can be explained by lightning or dry storms, but others only make sense if they are intentional," he said.

In neighbouring Portugal, firefighters were battling three large wildfires in the centre and north of the country.

The largest, near the town of Trancoso, has been burning since Saturday and is being bttled by more than 650 firefighters backed by six aircraft.