Portugal declared three days of national mourning on Sunday for 61 victims of forest fires on the weekend.

Many were found dead inside their cars as they tried to flee the central forested region of Pedrógão Grande.

Four children are among the deceased.

Thousands of firefighters rushed to the stretch of road between Figueiró dos Vinhos and Castanheira de Pera in central Portugal.

They continue to tackle the flames.

Portigal’s prime minister Antonio Costa called the blaze:

The greatest tragedy we have seen in recent years in terms of forest fires.

The cause of the fire was thought to have been a lightning strike during a dry thunderstorm, he said.

The fire spread along four fronts with “great violence,” said Jorge Gomes, Portugal’s secretary of state for internal administration.

The homes of residents living in the vicinity of the flames have been destroyed by the fire.

Last August, a blaze engulfed parts of Portugal, including the Madeira islands in the Atlantic, where the flames reached the main city, Funchal.