Local officials said the fire damaged power lines, causing blackouts and water supply outages in many areas after nightfall.
"The coming night will be especially difficult ... We urge people to remain calm and not panic"
Yiannis Kapakis, a fire service spokesman
A number of homes have been destroyed and thousands of hectares of forest and farmland burnt.
Olive groves and forests in the hills outside the town, north-east of Athens, have already been destroyed.
Firefighters have urged people to evacuate their homes, but many residents have stayed to defend them.
"Firefighters are working in extremely difficult circumstances,'' Costas Karamanlis, Greece's prime minister said.
"Our priority is the protection of human life and property."
Winds are expected to drop overnight but are forecast to reach gale force again on Sunday.
|Authorities have declared a state of emergency, till the blaze is under control [AFP]
Authorities are worried that the fires will rage through the night because firefighting planes and helicopters will stop operating at dusk.
"The coming night will be especially difficult,'' Yiannis Kapakis, a fire service spokesman, said.
"We urge people to remain calm and, in any case, not panic.''
He said 75 fires had broken out across Greece since early Saturday morning - including blazes on the island of Evia, Skyros and Zakynthos as well as in parts of central and southern Greece.
As night fell, 12 planes, eight helicopters, about 80 ground vehicles and nearly 600 soldiers were trying to contain the fire north of Athens, he said.
"We keep sending in more planes, helicopters and ground vehicles. Volunteers constantly arrive with more vehicles. The army is also involved,'' Kalpakis said.
The Greek Army confirmed that anti-aircraft missiles had been evacuated from a base near Marathon.