Thick clouds of smoke darkened the sky over Mount Penteli where the fire broke out on Tuesday, some 27 kilometres north of central Athens.
There were no reports of injuries, the fire brigade said.
About 485 firefighters and 120 fire engines were deployed to try to tame the blaze, which was burning on several fronts.
Several helicopters and planes were dumping water on the flames, though they had halted operations during the night for safety reasons.
"It was a difficult night," said Fire Department spokesperson Yiannis Artopios in a televised statement, adding that the wind speed exceeded 80km/h.
"Due to the intensity and speed of the winds, the fire constantly changed direction throughout the night, which made fighting it, in the middle of the night, even more difficult," he said.
Local authorities said the fire had burned some homes in the area of Pallini. The fire brigade would not confirm the information.
Authorities had ordered the evacuation of nine areas, including Pallini and Gerakas.
One hospital and the National Observatory of Athens had been evacuated as a precaution. Traffic was halted on roads leading to Penteli and police helped at least 600 residents to find their way out of the fire-stricken areas.
Strong winds were forecast to persist until Wednesday afternoon.
The fire brigade said that 28 firefighters from Romania were assisting local firefighters. More than 200 firefighters and equipment from Bulgaria, France, Germany, Romania, Norway and Finland will be on standby during the hottest months of July and August in Greece.
Last year, wildfires ravaged about 121,000 hectares of forest and bushland in different parts of Greece as the country experienced its worst heat wave in 30 years.
