Orange flames engulfed pine forests, turning them to ash and leaving lines of charred cars in the smoke-filled streets of seaside towns near Athens after the fires broke out on Monday.
Rescuers rushed to evacuate residents and tourists stranded on beaches.
Others were overtaken by the flames in their homes, on foot or in their cars.
AFP photographers saw burnt bodies of humans and dogs.
The charred bodies of 26 people, including small children, were discovered in the courtyard of a villa at the seaside resort of Mati, 40km (25 miles) northeast of the capital, said rescuer Vassilis Andriopoulos.
They were huddled together in small groups, “perhaps families, friends or strangers, entwined in a last attempt to protect themselves as they tried to reach the sea”, he said.
“The problem is what is still hidden under the ashes,” said vice-president of Emergency Services Miltiadis Mylonas.
The government said that 308 engineers will arrive on site by today to assess the damage.
Video footage showed people fleeing by car as the tourist-friendly Attica region declared a state of emergency.
“I saw the fire move down the hill around 6pm and 5-10 minutes later, it was in my garden,” said 60-year old Athanasia Oktapodi.
Her home is surrounded by dry pine trees.
“They caught fire. I ran out like a crazy person, got to the beach and put my head in the water. Then the patrol boats came.”
Fire service spokeswoman Stavroula Maliri raised the overall death toll yesterday to 74 from an earlier count of 60.
She said that the toll was not yet final since firefighters were still searching for victims.
We continue to receive “dozens of calls” from people looking for relatives, she said.
Winds of more than 100kph (60mph) in Mati caused a “sudden progression of fire” through the village, said Maliri.
“Mati no longer exists,” said the mayor of nearby Rafina, Evangelos Bournous.
He added that more than a thousand buildings and 300 cars had been damaged.
According to Maliri, 82 people remained in hospital last night, including 10 adults needing respiratory assistance.
Officials said that they were Greece’s deadliest blazes in more than a decade.
At least six people died trying to escape the flames into the sea.
Some 715 people were evacuated by boats to Rafina, the government said.
“People are shocked, lost. Some of them have lost everything: children, parents, homes,” said Red Cross spokeswoman Georgia Trisbioti.
Greece’s Prime Minister Alexis Tsipras cut short a visit to Bosnia to return home.
He announced three days of national mourning.
Anticipating questions about the high death toll and the emergency planning, Tsipras stressed the “extreme” scale of the fires.
Government spokesman Dimitris Tzanakopoulos said that “15 fires had started simultaneously on three different fronts in Athens” on Monday.
The European Union activated its Civil Protection Mechanism after Greece sought help.
Several countries said they were sending aircraft to help fight the flames.
European Commission chief Jean-Claude Juncker tweeted yesterday that the EU “will spare no effort to help Greece and the Greek people”.
Tsipras said “all emergency forces” have been mobilised to battle the fires.
Interior Minister Panos Skourletis said yesterday that the priority is to extinguish a fire that was still burning in Kineta, 50km from Athens.
Near the town of Marathon, residents fled to safety along the beach, while 600 children were evacuated from holiday camps in the area.
Officials raised the possibility the blazes could have been started deliberately by criminals seeking to ransack abandoned homes.
“I am really concerned by the parallel outbreak of these fires,” Tsipras said.
Supreme Court prosecutors announced they had opened an investigation into the causes of the fire.
Fires are a common problem in Greece during the summer.
Blazes in 2007 on the southern island of Evia left 77 people dead.
Temperatures have climbed to 40° Celsius (104° Fahrenheit) but showers and falling temperatures were expected later in Athens.
Wildfires have also caused widespread damage in northern Europe in recent days.
Sweden is experiencing an unprecedented drought and the highest temperatures in a century.
It has counted more than 20 fires across the country.
In Finland’s northernmost Lapland province fires have ravaged woods and grassland close to the border with Russia.
Norway, which experienced its hottest May temperatures on record, has also seen several small fires.
One firefighter was killed on July 15 trying to contain a blaze.
Fires have raged for five days in Latvia, destroying more than 1,000 hectares in the Baltic state’s western regions.
The German Meteorological Service DWD warned of a significant risk of fires in fields and forests due to drought.
In the Netherlands, a wildfire broke out over about four hectares yesterday in the central nature reserve of Hoge Velume, known for its red deer and wild boar, Dutch media said.
The fire brigade brought the blaze quickly under control.
