An official said most of the victims "burned to death in their cars when they found themselves trapped by flames on the road from Figueiro dos Vinhos to Castanheira de Pera."
The death toll in forest fires raging in central Portugal has reached 62, the government said on Sunday. Government officials said many of victims died in their cars when flames swept over a road.
"The dimension of this fire was such that we don't have memory of such a human tragedy," Prime Minister Antonio Costa said as he arrived in Pedrogao Grande, a mountainous area some 150 (95 miles) kilometres northeast of Lisbon.
He said it was vital to focus on the prevention of new fires amid a continuing heat wave, strong winds and lack of rain. He also warned that the death toll could still increase.
TRT World's Nafisa Latic has more.
Three days of mourning
The government declared three days of mourning and sent two army battalions to help the emergency services.
The European Union said it would provide firefighting aircraft. France has offered three planes and Spain has sent two, authorities said.
Speaking in the Vatican, Pope Francis, who visited Portugal last month, mentioned the victims in his weekly address: "I am close to the dear people of Portugal, hit by a devastating fire which is raging in the forests around Pedrogao Grande, causing many victims and injuries. Let us pray in silence."
Around 600 firefighters and 160 vehicles were dispatched to tackle the blaze, which broke out on Saturday afternoon in the municipality of Pedrogao Grande before spreading.
"Unfortunately, this seems to be the greatest tragedy we have seen in recent years in terms of forest fires," a visibly moved Costa said earlier at the Civil Protection headquarters near Lisbon.
"The number of fatalities could still rise," he said.
"The priority now is to save those people who could still be in danger."
"France has offered three planes through the EU Civil Protection Mechanism and they will be quickly sent to assist the local emergency efforts," EU Commissioner for Humanitarian Aid and Crisis Management Christos Stylianides said.
Neighbouring Spain's prime minister also offered support to Portugal. Mariano Rajoy tweeted that he is "overwhelmed by the tragedy at Pedrogao Grande. The Portuguese people can count on our solidarity, support and care."
Portuguese Prime Minister Antonio Costa said that Spanish rescuers would assist in efforts to control the blazes.
My thoughts are with the victims in #Portugal. I commend the bravery of the firefighters.EU civil protection mechanism activated & will help— Jean-Claude Juncker (@JunckerEU) June 18, 2017
French President Emmanuel Macron said in a Twitter message: "Solidarity with Portugal, hit by terrible fires. Our thoughts are with victims. France makes its aid available to Portugal".
Suffocation and incineration
Interior ministry official Jorge Gomes earlier said all 19 of the people then confirmed dead were civilians.
"Three of them died from smoke inhalation and 16 burned to death in their cars when they found themselves trapped by flames on the road from Figueiro dos Vinhos to Castanheira de Pera," Gomes told journalists.
Fourteen civilians were injured, 10 of them seriously, along with six firefighters, he added.
The flames spread "with great violence", moving out on four fronts, he said. Several villages were affected by the blaze but Gomes was not immediately able to comment on the extent of the damage caused.
Portugal's President Marcelo Rebelo went to the Leiria region to meet families of the victims, "sharing their pain in the name of all the Portuguese people," he said. Firefighters did "all they could" when faced with the blaze, he added.
Avelar resident Isabel Brandao blamed it on the lack of rain. "The problem is that there was no rain. If it had rained, this would not happen."
Brandao said that "at 3:30 am my mother-in-law woke me up quickly and we never went to sleep again. We were afraid the fire would reach us."
Portuguese authorities say that they are still investigating the cause of the fire. But Prime Minister Antonio Costa said high temperatures of 40 C (104 F) in recent days may have played a part.
Portugal was sweltering under a severe heat wave Saturday.
The country was hit by a series of fires last year which devastated more than 100,000 hectares (1,000 square kilometres) of the mainland.
This is a developing story and will be updated accordingly.