A huge wall of thick smoke and bright red flames towered over the tops of trees in the forested Pedrogao Grande area, 150 kilometers (95 miles) northeast of Lisbon where a lightning strike was believed to have sparked the blaze Saturday. Investigators found a tree that was hit during a "dry thunderstorm," the head of the national judicial police said.
Dry thunderstorms are frequent when falling water evaporates before reaching the ground because of high temperatures. Portugal is prone to forest fires in the dry summer months and temperatures as high as as 40 degrees Celsius (104 Fahrenheit) hit the area in recent days.
At least four other significant wildfires were burning Sunday elsewhere in Portugal but the one in Pedrogao Grande was responsible for all the deaths.
"The dimensions of this fire have caused a human tragedy beyond any in our memory," said Prime Minister Antonio Costa told reporters as he arrived at the scene Sunday. "Something extraordinary has taken place and we have to wait for experts to properly determine its causes."
He said the death toll was lowered to 61 from 62 because one person had been counted twice. However, he added "there's no point in feeling joyful for that, because surely we will find more victims as we progress."
Interior Ministry official Jorge Gomes said firefighting crews were having difficulties battling the fire, which was "very intense" in at least two of its four fronts. He said authorities were worried about strong winds that could help spread the blaze further.
More than 350 soldiers on Sunday joined the 700 firefighters who have been struggling to put out the blaze, schools in the area were closed until further notice and outdoor fires were banned.
The forest fire deaths were the biggest in memory in Portugal, which saw 25 Portuguese soldiers die fighting wildfires in 1966. Last August, an outbreak of fires across Portugal killed four people, including three on the island of Madeira, and destroyed huge areas of forest.
Isabel Brandao told The Associated Press on Sunday that she had feared for her life when she saw the Pedrogao Grande blaze.
"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."
Others were also shocked.
"This is a region that has had fires because of its forests, but we cannot remember a tragedy of these proportions," said Valdemar Alves, the mayor of Pedrogao Grande. "I am completely stunned by the number of deaths."
State broadcaster RTP showed terrifying images of several people on a road trying to escape the intense smoke that had reduced visibility to a few meters (yards). A young man shared a bottle of water with a distraught woman as she stumbled down the road.
Gomes gave a grim description of the deaths to RTP. He said at least 30 people died inside their cars as they tried to flee between the towns of Figueiro dos Vinhos and Castanheira de Pera. He said 17 others died right outside their cars or by the road, 11 people died in the forest, two people died in a car accident related to the fire and information was missing on the other deaths.
Gomes said 54 people were also injured in the fire, 5 of them seriously, including four firefighters and a minor.