AVELAR, Portugal -- A raging forest fire in central Portugal sent flames sweeping over roads, killing at least 62 people, many of them trapped in their cars as they tried to flee, officials said Sunday. The country's prime minister called it "the biggest tragedy" that Portugal has experienced in decades and declared three days of national mourning.

A huge wall of thick smoke and bright red flames towered over the top of trees in the forested Pedrogao Grande area some 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 told Portuguese media.

Dry thunderstorms are frequent when falling water evaporates before reaching the ground because of high temperatures. Portugal, like most southern European countries, is prone to forest fires in the dry summer months. At least four other significant wildfires affected different areas of the country on Sunday but the one in Pedrogao Grande was responsible for all the deaths.

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"The dimensions of this fire have caused a human tragedy beyond any in our memory," said Prime Minister Antonio Costa told reporters on his arrival at the scene Sunday. "Something extraordinary has taken place and we have to wait for technicians to properly determine its causes."

He said the death toll was lowered from the previously reported 62 victims because one person had been counted twice.

More than 350 soldiers on Sunday joined the 700 firefighters who have been struggling to put out the blaze. Authorities say temperatures as high as 40 degrees Celsius -- 104 Fahrenheit -- in the area in recent days might have also played a part in the inferno.

A forest fire is seen near Tojeira, Pedrogao Grande, in central Portugal, on Sun., June 18, 2017. Reuters

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.

Resident Isabel Brandao told The Associated Press that she had feared for her life when she saw the blaze.

"Yesterday we saw the fire but thought it was very far. I never thought it would come to this side," she said Sunday. "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."

Other locals 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 yards. A young man shared a bottle of water with a distraught woman as she stumbled down the road.

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 spreading the blaze further.

Schools in the area were closed until further notice and outdoor fires were banned, authorities announced Sunday.

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 says 17 others died right outside their cars or by the road, 11 people died in the forest and two people died in a car accident related to the fire and information was missing on the other deaths.

So far, no one has been reported killed by the fire inside a house.

Gomes says 54 people were also injured in the fire, 5 of them seriously, including four firefighters and a minor.

Costa tweeted his "deepest regret for the victims ... and a word of encouragement and strength for all who help combat this scourge."

"We are most likely facing the biggest tragedy of human life that we have known," he said.

There was no immediate identification of the victims. Portugal established a special diplomatic channel for embassies to receive information on foreign citizens who "may be affected" by the fire.

The European Union responded to a call for assistance by Portuguese authorities. As a result, Spain sent four firefighting aircrafts on Sunday. France was also sending three aircraft and Greece's prime minister also offered to send firefighting help.

Many world leaders, including French President Emmanuel Macron, Pope Francis and Indian Prime Minister Narendra Modi, expressed solidarity with Portugal. Spanish Prime Minister Mariano Rajoy tweeted that he is "overwhelmed by the tragedy at Pedrogao Grande. The Portuguese people can count on our solidarity, support and care."

In Kazan, Russia, Portugal's national soccer team wore black arm bands and stood for a moment of silence with the Mexican team in solidarity with the forest fire victims. The ceremony took place before the teams' match Sunday at the Confederations Cup tournament.

Coach Fernando Santos, Cristiano Ronaldo and the rest of the players released a statement saying "in this sad hour, we send our deepest sympathies to the families, friends and loved ones of the victims of the fires."

FIFA President Gianni Infantino, attending the match in Russia, also offered his condolences.

"We want to send a big hug to everyone in Portugal for what they are going through, which is absolutely terrible. There are no words for that," he told reporters.