Spain's worst wave of wildfires in at least two decades spread to the southern slopes of the Picos de Europa mountain range on Monday and prompted authorities to close part of the popular Camino de Santiago pilgrimage route.

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.

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.

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 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.

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.

Joaquín Ramírez of Technosylva, a Spanish company that specialises in prevention and response to wildfires, attributed this year’s litany of fires to “a combination of abandonment of rural areas, abandonment of managing [the land] and the stress exerted on our forest areas”.

Spain still faces "difficult hours" ahead in its fight against wildfires that have ravaged a record area of land, Prime Minister Pedro Sanchez warned Tuesday, despite the onset of cooler weather.The most intense heat,