The fire started mid-morning and raced down the Penteli mountain, 20km north of the Greek capital, sending a dark cloud across the city, blocking out the sun and leaving the smell of charred wood hanging in the air.
Residents of the Melisia, Vrilisia and Penteli suburbs could do nothing but watch helplessly as 30m-high flames engulfed their homes.
Others packed their belongings into cars and fled for fear of being cut off by the fire.
'A huge catastrophe'
Manolis Grafakos, Melisia's mayor, said: "This is a huge catastrophe. There are no words to describe it. A large chunk of the forest is gone, houses have been burnt and I do not think we are fully aware of the extent of the damage."
Gale force winds prevented aircraft from joining the firefighting operations earlier in the day, allowing it to get out of control, the fire brigade said.
Fire brigade officer Nikolaos Diamantis said: "From 11 to 12:30 the airplanes could not operate due to strong winds and thick smoke."
He said the fire had started simultaneously at four points in the forest, about 500m apart.
More than 60 fire engines, 19 aeroplanes and helicopters as well as hundreds of firefighters and volunteers were tackling the blaze.
A private clinic, a hospital and a summer camp in the area were also evacuated as a precaution, police said.
Residents, who accused state agencies of responding slowly, said several homes had burnt down with no sign of the fire stopping.
One Penteli resident, in tears, told Greek television: "There is no power, no water and no help. Our houses are doomed."
Greece has seen some of the worst fires of the past 10 years this summer, caused by record-high temperatures, drought and arsonists.
In late June, the biggest national park near the city, on Mount Parnitha, burned for three days leaving more than a third of the nature reserve charred.