Most died while trying to flee the Pedrógão Grande area, 50 km (30 miles) south-east of Coimbra, in their cars, according to the government, BBC reports.
Hundreds of firefighters are continuing to tackle the blaze, which has spread across several fronts.
Prime Minister Antonio Costa called it "the greatest tragedy we have seen in recent years in terms of forest fires".
The death toll could rise further as many people remain missing, he warned. The authorities have declared three days of national mourning, starting on Sunday.
Secretary of State for the Interior Jorge Gomes said that the majority of the victims died from smoke inhalation and burns, while two died in a road accident related to the fires.
He earlier said 30 bodies were found inside cars, with another 17 next to the vehicles, on one road leading on to the IC8 motorway.
Another 11 died in a village next to the motorway.
Media in Portugal say the fire is no closer to being contained despite hundreds of firefighters and 300 vehicles working to put it out.
Among the dozens of people injured was an eight-year-old girl with burns found wandering alone close to the fire, the Correio do Manhã newspaper reported.
Six firefighters are seriously wounded, national broadcaster RTP said, and two who went missing overnight turned up injured.
Read alsoLarge-scale fire raging outside Kyiv as fuel depot bursts out (Photos)The Correio do Manhã warned that many areas hit by the fire had not yet been reached by authorities, so the death toll was likely to increase.
About 60 forest fires broke out across the country overnight, with close to 1,700 firefighters battling them across Portugal.
The flames spread "with great violence" on four fronts near Pedrógão Grande, Mr Gomes said.
Spain has sent two water-bombing planes to help tackle the fires, and the European Union is co-ordinating an international firefighting and relief effort.
It is not yet known what caused the fire, however Mr Costa said thunderstorms could have been one possible cause.
Portugal has been experiencing a heatwave, with temperatures of more than 40C (104F) in some areas.
"This is a region that has had fires because of its forests, but we cannot remember a tragedy of these proportions," Valdemar Alves, the mayor of Pedrógão Grande, was quoted as saying by the Associated Press agency.
"I am completely stunned by the number of deaths."
There were very particular circumstances with the lightning strikes here - this fire started with a dry lightning strike. There has been rainfall elsewhere but there was no rain there, and this is a heavily-forested area.
Getting it under control depends not only on temperatures, which do seem as though they will be high, but on the wind above all. It is very much in the hands of Mother Nature.