Around 700 firefighters are battling the inferno, which began on Sunday about 20 miles from Athens, officials said.
An “exceptionally dangerous” forest fire has raged out of control in Athens, sending flames 25 metres (80ft) into the air.
The massive blaze, helped by strong winds and bone-dry conditions, has forced many people in the northern suburbs of the Greek capital to leave their homes.
Hospitals have been evacuated and some areas have suffered power cuts, as temperatures neared 40C (104F).
Thousands of people fled their properties, including in the historic town of Marathon, following numerous evacuation orders as a blanket of smoke and ash covered the city centre.
Residents have complained of not being able to breathe properly and finding the smoke “suffocating”.
Around 700 firefighters are battling the flames, which began on Sunday about 20 miles from Athens.
Flames have engulfed an area of about 20 miles. By Monday afternoon, the fire had reached a suburb around nine miles from the centre.
More than 190 vehicles have been used, along with 17 water-dropping planes and 16 helicopters providing aerial support.
Three hospitals, including a children’s hospital, two monasteries and a children’s home were evacuated.
Police said 380 officers were assisting in evacuations, and helped move more than 250 people away from the path of the flames.
Two firefighters were injured – one was treated for light burns and the other for breathing problems – and 13 civilians suffered breathing difficulties.
It was “an exceptionally dangerous fire, which we have been fighting for more than 20 hours under dramatic circumstances”, climate crisis and civil protection minister Vassilis Kikilias said.
Mr Kikilias said the fire was burning mainly on two separate fronts, including in hard-to-reach areas on a mountain to the northeast of Athens, adding that half of the country is currently under a “red alert” for wildfire hazard.