Witnesses have reported whole towns have been razed to the ground by the blaze, thought to be the country's most deadly fire in more than a decade.
Authorities believe dozens are dead, including 26 people found across just two villas in the village of Mati by Greek Red Cross relief workers.
More than 100 others have been reported injured while fleeing the fires, including 11 understood to be in a serious condition.
Follow our live updates for all the latest news from Athens:
Authorities in Greece say the blaze has now claimed the lives of 60 people.
Evangelos Bournous, the mayor of the fire-hit town of Rafina, around 16 miles east of Athens, told Skai TV: "The number of dead is rising, it has already exceeded 60."
If you are just joining this developing story, here is the latest from Athens are firefighters battle several deadly blazes close to the Greek capital.
At least 60 people are now thought to have died and dozens others have been injures as wildfires have swept through several tourists resorts.
Many had to run to beaches, where they were evacuated by waiting boats, in a bid to escape the approaching flames.
In the village of Mati, some 26 bodies were found by Greek Red Cross workers across just two villas.
Meanwhile, more than 100 other people are thought to have been injured by the fires, including 11 who are in a serious condition in hospital.
Greek prime minister Alexis Tsipras has cut short a trip to Bosnia to return to Athens amid the growing disaster his country faces.
“We are dealing with something completely asymmetric,” he told reporters on Monday evening. “It's a difficult night for Greece.”
One Twitter user has shared incredible footage of the dozens of wildfires authorities are trying to contain as seen from an aeroplane.
Dimitris Tzanakopoulos, spokesman for the Greek government, has said 156 people have now been hospitalised after being injured during the fires.
“The situation is still critical,” he said on Tuesday afternoon. “Beyond the firefighting operation, a contingency plan with the input of many ministries has been implemented.”
“Since yesterday, all available units of the Ministry of Health have been mobilised in Attica,” he added.
“In particular, there were continuously available 38 ambulances, four mobile units and two special disaster response units.”
Prime minister Alexis Tsipras has announced a national mourning period of three days for the dozens of people who have lost their lives during the wildfires.
“The country is going through an unspeakable tragedy,” he said on Tuesday in a televised address.
“Today, Greece is mourning and we are declaring three days of national mourning in the memory of those who perished.”
The Greek leader last called a period of national mourning in November 2017, when flash flooding in the Attica region left more than a dozen people dead.
The UK's ambassador to Greece, Kate Smith, has sent her condolences to the people affected by the wildfires in a message on Twitter.
The news and images from the fires in Attica are disheartening. Those on the front line, they fought a real battle. A tragic day for Attica and Greece. Our sincere condolences.
Meanwhile, the US ambassador to Greece, Geoffrey Pyatt, has also offered his condolences to the people of Greece.
A survivor of the fire in the village of Mati that appears to have alone claimed the lives of more than 20 people has spoken of the terrifying ordeal of escaping the blaze.
Nikos Stavrinidis had gone to his summer home in Mati to prepare it for his student daughter, who was coming to stay, before fire suddenly engulfed the house.
He said he and five other people had to drive into the sea and swim in order to avoid the smoke, getting dragged out by the current in the process.
Mr Stravrinidis said a child in their group died in the water:
It happened very fast. The fire was in the distance, then sparks from the fire reached us. Then the fire was all around us.
We ran to the sea. We had to swim out because of the smoke, but we couldn't see where anything was.
We didn't all make it. What upsets me and what I will carry in my heart is that it is terrible to see the person next to you drowning and not be able to help him.
You can't. That's the only tragic thing. That will stay with me.
A tweet from the account of Greek PM Alexis Tsipras had called for citizens to “stand with unity and faith” with those carrying out relief and rescue efforts.
“Greece is going through a great ordeal,” he adds.
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