At first light, air water bombers resumed operations over the towns of Mandra, west of Athens, and Loutraki, close to the Corinth canal which separates mainland Greece from the Peloponnese. Firefighters worked throughout the night to keep flames at bay and away from a complex of coastal refineries.
Four aircraft sent from Italy and France will join the efforts on Wednesday, authorities said.
The fire brigade reported that a third fire had broken out on the island of Rhodes.
Dozens of homes were gutted and hundreds forced to flee towering flames which seared through hamlets on Tuesday. Traffic was suspended for hours on two roads connecting the mainland to the Peloponnese. They were partially reopened early Wednesday.
The fire risk hazard was high throughout the country. "We remain on a level of high alert," said fire brigade spokesman Vassilis Varthakogiannis.
The Greek meteorological service has warned of a high risk of fires this week, just as the country recovers from the first major heatwave of the summer. A second heatwave was forecast to start on Thursday.
"Conditions are extreme, and are likely to be so for another week," Kostas Tsigas, head of the fire brigade officers association, told Greece's SKAI TV.
The blaze, which broke out on Monday in the region of Dervenochoria, about 30 km north of Athens, spread fast as it was fanned by erratic winds and reached Mandra on Tuesday, burning houses and forcing people to flee.
Not everyone went willingly. Footage released by Greek police showed officers imploring a reluctant group of nuns chanting hymns to evacuate a convent, and another of police screaming "lets go" as towering flames closed in at a timber yard.
"We put all our effort into making this, we built this, and now it's all gone," said Andreas Theodosiadis, a resident of Mandra, standing near debris and cars hollowed out by fire.
The broader region has had bitter previous experience with natural disasters. In 2017, Mandra, a largely industrial area, was hit by flash floods that killed 24 people. A year later, 101 people died in the seaside town of Mati, east of Athens, after a wildfire razed the town in a matter of hours.
