The European Union has sent two firefighting planes to Spain to help battle raging wildfires, after the country activated the bloc's disaster assistance mechanism for the first time.

The assistance comes as the country recorded a third wildfire-related death on Thursday morning.

There are concerns the wildfires could continue to spread. Spain's state weather agency Aemet forecasts that a heatwave will continue until Monday, with temperatures of up to 44C in some areas, as well as moderate winds.

Spain is the fifth European nation to request assistance with fighting wildfires. In Greece, 25,000 acres of land have burned since Tuesday.

Two French Canadair water bomber aircraft arrived in Spain's north-western Galicia region on Thursday.

"The fight against fires knows no borders," government representative in the region Pedro Blanco said. "French resources are now in Spain to intensify efforts to extinguish forest fires."

Interior Minister Fernando Grande-Marlaska told local media on Wednesday that the two planes were not yet needed, but that the government wanted them in Spain so they could be put to use when necessary.

He told broadcaster Cadena SER that he had not ruled out requesting more firefighters.

A volunteer firefighter died in hospital in the north-western region of León on Thursday, after suffering severe burns.

He became the second volunteer to die as a result of a fire in the region and the third person to die in total. Another man died near the capital, Madrid, last Tuesday.

"We are struck once again by the death of a second volunteer who has lost their life in León," Prime Minister Pedro Sanchez said on Thursday. "All our love and support go out to their family and friends during this unbearable time."

Spain's Civil Guard said it had arrested two men on suspicion of starting fires in Castille and León that had spread across thousands of hectares - taking the number of arson arrests to 10 since the start of June.

While weather conditions are currently favourable for wildfires, they can be sparked by barbecues, cigarette stubs or discarded bottles. Causing a wildfire is a criminal offence in Spain, even if unintentional.

Thousands of people have been evacuated from their homes across the country, with 700 told to leave their towns in the south-western province of Caceres on Wednesday.

In neighbouring Portugal, more than 1,900 firefighters have been deployed to tackle four major blazes, with one in the central city of Trancoso already burning an estimated 14,000 hectares since Saturday, AFP news agency reported.

The government also extended a state of alert issued last week for the entire mainland to Sunday.

Wildfires are a common occurrence across southern Europe in the summer, but their severity can often be exacerbated by heatwave conditions.

EU data shows that around 629,000 hectares (1.6 million acres) of land has burnt across the bloc since the beginning of the year, with wildfires in Spain comprising around a quarter of that total.

While linking climate change with individual extreme weather events can be difficult, scientists say that climate change is generally making heatwaves hotter, longer and more frequent.

Prolonged hot conditions can dry out the ground and vegetation, making it easier for wildfires to spread rapidly.

Greece, Bulgaria, Montenegro and Albania have also activated the EU's civil protection mechanism, which allows any country hit by a disaster - both in Europe and beyond - to request emergency assistance.

In Greece, wildfires have been burning for a third consecutive day, with the most dangerous fronts on the island of Chios and in the Achaia region of the Peloponnese.

So far, 95 people - including both firefighters and civilians - have been injured.

EU data shows that more than 10,000 hectares (25,000 acres) have burned across the country since Tuesday morning.

Authorities have issued a red alert for Thursday, warning of very high fire risk in Attica, eastern Central Greece, Evia, the north-eastern Peloponnese, and Thrace.

In Chios, the fire's front stretched for dozens of kilometres, and with limited resources available, many residents have had to be evacuated by sea using coastguard and private vessels.

Authorities said three men had been arrested for a fire near the port city of Patras, which began earlier this week and pockets of whcih continue to burn.

Fires have also raged in Albania and Turkey, with several firefighters injured while tackling the blazes.

Additional reporting by Nikos Papanikolaou in Greece