At least five more communities were told to flee by civil protection authorities, after hundreds of people evacuated Sunday from at least eight villages.
"Civil protection forces battled hard throughout the night, but despite superhuman efforts, the fire evolved rapidly," fire brigade spokesman Vassilis Vathrakogiannis said.
"At this moment it has reached Mount Pentelicus and is headed in the direction of Penteli," he added.
Two hospitals in Penteli -- one for children and a military facility -- were evacuated at dawn according to Vathrakogiannis.
The brigade has deployed 510 firefighters and 152 vehicles, while 29 aircraft were due to set out at first light, he added.
"Forest fire near you. Follow the instructions of the authorities," said SMS messages sent to people in the Attica region, indicating in which direction to flee.
Prime Minister Kyriakos Mitsotakis cut short his holiday and returned to Athens Sunday evening to deal with the crisis.
By Sunday afternoon, firefighters had quickly dealt with 33 out of the 40 blazes that had broken out in the past 24 hours.
But the force was battling seven more in the high Mediterranean summer heat, the fire brigade spokesman said Sunday.
Residents of the historic town of Marathon, 40 kilometres (25 miles) east of Athens, were among those ordered to evacuate Sunday.
"Everything is burning," said Giorgos Tsevas, a resident of Polydendri village.
"I have 200 olive trees there but now they are gone," the 48-year-old said Sunday.
Already Saturday, Civil Protection Minister Vassilis Kikilias had warned that half the country was under a high-risk warning for fires due to high temperatures, wind gusts and drought conditions.
"Throughout the night, winds remained strong, creating dangerous situations. Unfortunately their intensity is expected to increase in the coming hours," Vathrakogiannis warned.
The Mediterranean country is exceptionally vulnerable to summer blazes, with this season seeing fires burn daily.
After the warmest winter on record, Greece also experienced its hottest June and July since reliable data collection began in 1960.
Scientists warn that human-induced fossil fuel emissions are worsening the length, frequency and intensity of heatwaves across the world.
The rising temperatures are leading to longer wildfire seasons and increasing the area burnt in the flames, according to the United Nations Intergovernmental Panel on Climate Change.
