Wildfires west and north-west of Athens continued to spread on Sunday, with flames advancing to within a few kilometres of Megara, according to local media.
The most serious blaze is burning in the Cithaeron mountain range, where strong winds are driving the fire eastwards.
Megara, a town about 50km west of Athens, is now under growing threat. Areas around the communities of Veniza and Psatha have also been badly affected.
Evacuation alerts have been issued in several places through the emergency warning system.
Overnight from Saturday to Sunday, several hundred firefighters were deployed to tackle the blaze, supported by volunteers and military vehicles.
At first light, firefighting aircraft and helicopters were also sent in, state broadcaster ERT reported.
News website Protothema estimated that 10,000 hectares have already been destroyed by the fires in the wider region to the west and north-west of Athens.
Elsewhere, another forest fire is burning on the island of Kefalonia, although no villages are currently under threat there.
Local media said wildfires on Crete have been almost completely brought under control.
A fire service spokesperson said 13 people had been arrested across Greece on suspicion of causing fires through negligence.
