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.

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

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 key to preventing forest fires is creating a rural economy based on the use of forests. While this would generate much-needed employment in “la España vaciada” – “hollowed-out Spain”, the name given to the country’s depopulated rural areas – it also costs money. It is therefore essential to invest in forests.

Thousands of firefighters worked overnight to contain dozens of deadly wildfires burning across Spain and Portugal as heat and gusty winds spread blazes through dry brush, forests and crops.

Spain deploys 500 additional soldiers to fight devastating wildfires as extreme heat fuels blazes across Europe.

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.

A second volunteer firefighter has died after battling a wildfire in the northern Spanish province of Leon, while police arrested a man for allegedly starting a separate blaze as the country faced one of its worst summers for fires in 20 years.

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.