Cooler conditions are helping Spanish and Portuguese firefighters tackle deadly blazes that have forced tens of thousands of people to flee over the past two weeks.

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.

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.

Firefighters have spent days battling blazes in Greece, Portugal, Spain and elsewhere. Forecasters said temperatures could pass 111 degrees in some places on Thursday.

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.

Spain has been hit by a heatwave with the mercury hitting 32C in Seville this week and highs of 35C in Madrid and 31C in Barcelona. The UK has also been issued a yellow heat health warning

Spain has endured the worst fire season on record, with devastating blazes continuing to destroy homes and land across the country.