Spain is deploying 500 more soldiers to help battle wildfires that have ravaged parched woodlands during a prolonged heat wave, Prime Minister Pedro Sánchez said.

The fires have spread over the regions of Extremadura, Galicia, and Castile and Leon, forcing authorities to suspend rail services and cut access to roads in the area, as well as blocking a 50-kilometre stretch of the popular Camino de Santiago pilgrimage trail.

Spain's worst wave of wildfires on record spread to the southern slopes of the Picos de Europa mountains on Monday and prompted authorities to close part of the popular Camino de Santiago pilgrimage route.

Firefighters in Spain, Portugal and Greece battled ongoing wildfires Friday, an important religious holiday in all three countries, as persistent hot, dry conditions challenged efforts to contain the blazes.

This year is turning into one of the worst fire seasons in recent memory in Europe. Firefighters are struggling to contain out-of-control wildfires in western Spain and Portugal.

Spain's weather agency warned the public on Monday to be "cautious" of the "very high or extreme fire danger."

According to the European Forest Fire Information System of the European Union, the fires in Spain this year has burned 158,000 hectares (390,000 acres). That's around the size of metropolitan London.

Europe’s next heat wave is already building over the Iberian peninsula, potentially testing more temperature records after an unseasonably cool start to August.

Spain on Friday warned of "very high or extreme fire danger in most of the country," as firefighters there continue battling 14 blazes in temperatures up to 104 degrees Fahrenheit.

Defence minister attributes fires to climate change, heat wave. The Interior ministry said 27 people have been arrested and 92 were under investigation for suspected arson since June.