Three days of national mourning, starting Sunda,y was declared by Prime Minister Antonio Costa.
'Unfortunately, this seems to be the greatest tragedy we have seen in recent years in terms of forest fires,' he said. 'The priority now is to save those people who could still be in danger.'
Officials say hundreds of firefighters have been dispatched to battle the blaze in the mountainous area of Pedrogao Grande, about 150 kilometers northeast of Lisbon.
Spain and France are sending aircraft to assist in efforts to douse the flames, authorities say. The European Union is also mounting an emergency assistance campaign.
"Unfortunately this seems to be the greatest tragedy we have seen in recent years in terms of forest fires," said Prime Minister Antonio Costa. The number of fatalities could rise, he added. "The priority now is to save those people who could still be in danger," the prime minister said.
Portuguese National Republican Guard firefighters work to stop a forest fire from reaching the village of Avelar, central Portugal, June 18 2017. A number of people have been killed in forest fires in central Portugal, many of them trapped in their cars as the fire swept over the road.
"The smoke cloud is very low, which does not allow helicopters and fire planes to work efficiently ... but we're doing everything possible and impossible to put out this fire," Jorge Gomes, secretary of state for the Interior, told Reuters, adding that no villages were currently at risk.
He said it was difficult to determine whether the people who burned in their cars "were fleeing the flames or were taken by surprise."
Local resident Isabel Brandao told The Associated Press that she had feared for her life.
"Yesterday we saw the fire but thought it was very far. I never thought it would come to this side," she said. "At 3:30 a.m., my mother-in-law woke me up quickly and we never went to sleep again. We were afraid the fire would reach us."