The Civil Protection Agency said 56 people were injured, 16 seriously, and nine were reported missing in the blazes that broke out over the weekend.

The fires returned to Portugal four months after a summer blaze claimed 64 lives in one night.

The year's current total of 99 deaths is far higher than the previous annual record of 25, in 1966.

The Civil Protection Agency said the figures were still provisional and were being assessed by the National Medical Emergency Institute (INEM) and the figures may change slightly as more information comes in.

Four people killed by the fires in Vouzela, near the northern city of Viseu early on Monday morning have added to the death toll from about 500 fires raging across Portugal over the weekend, officials said.

Previously, the death toll was six, but according to the mayor of Vouzela four people died early on Monday morning in this county, following a forest fire that devastated the parish of Ventosa.

According to the mayor, the four victims are all from the village of Ventosa, and three of them were found inside their houses and another on the road.

"For now there are four dead, but we are still assessing the situation. The fire also remains active," he said.

Six other victims had been previously recorded: two in Penacova (Coimbra district), one in Sertã (district of Castelo Branco), two in Oliveira do Hospital and one in Nelas (Viseu).

Around 500 fires across Portugal on Sunday also left 25 people injured, six of them in serious condition, and led to teh evacuation of several villages.

Speaking to journalists at the National Operations Command of the National Civil Protection Authority, in Oeiras, near Lisbon, at around 2.30 am, Prime Minister António Costa said he had declared a public calamity is for districts north of the River Tagus.

Almost 3,700 firefighters, backed by 1,100 vehicles, were fighting 26 major fires across the country at 2 am on Monday, according to the National Civil Protection Authority (ANPC).

October has been unseasonally warm, with temperatures in the high 30s Celsius over the weekend, and a severe drought has left land dry and at severe risk of fire. The ANPC said Sunday had been the worst day this year base don the number of fires that were active at the same time.

According to the official website of the ANPC, the biggest fire is in Lousã, Coimbra district, where 585 firfighters are working to put out the falmes, supported by 166 vehicles and one aircraft. This fire broke out at 8.40 am on Saturday and at 2 am it had two active fronts. The fire has cut traffic on the IP3 road between Santa Comba Dão and Coimbra.

A fire that broke out in Pedrógão Grande, in Leiria district, on 17 June claimed at least 64 lives and left more than 200 people injured. It was only finally extinguished a week later.

More than 2,000 fire fighters were called on to battle the flames, which consumed 53,000 hectares of forest – the equivalent of some 75,000 football pitches.