At least 74 people have died in wildfires near Athens, in the country's deadliest blazes in more than a decade.
Rescuers have found the bodies of 26 people who reportedly died in a coastal village earlier on July 24.
Blazes were reported to the west and the east of the Greek capital amid searing summer temperatures of 40 degrees Celsius and high winds.
Firefighters reported more than 100 people injured in the flames, some of them seriously, and said the death toll is expected to rise.
"Greece is going through an unspeakable tragedy," Prime Minister Alexis Tsipras said as he appeared on television to declare three days of national mourning.
Tsipras cut short a visit to Bosnia-Herzegovina to return to Greece, and asked the European Union and the military for help while ordering fire departments and emergency services in neighboring regions to the fire scenes.
The fire to the east quickly wiped out the village of Mati and in the port town of Rafina the flames moved from the outskirts into the town center, forcing hundreds of people to flee into the surf.
Extreme drought and strong winds fuelled the flames near the Greek holiday destination of Kinetan west of Athens, with smoke clouds billowing 40 kilometers to the east and reaching Athens.
The area is densely wooded and dotted with holiday homes.