A large wildfire broke out southeast of Athens on Sunday afternoon, amid warnings that the worst of the summer heat is yet to come.

Accustomed to scorching summers, Greece faces a tough wildfire season after its warmest winter and earliest heatwave on record, with temperatures hitting 44°C (111°F).

According to Athens News Agency, the fire started in Keratea district Sunday morning and was burning close to houses, while strong winds were blowing in the area.

Ertnews channel reported that at least three houses were completely destroyed by the fire.

Some 140 firefighters, with teams of forest commandos, 39 vehicles, eight helicopters and nine aircrafts were working to control the flames.

The emergency alert system 112 was activated, urging residents to evacuate from six areas in total near the capital.

It came a day after another wildfire had erupted in the same area, sparking evacuation orders but was later successfully controlled.

Separately, a large wildfire broke out on Serifos island on Saturday afternoon, but was also been brought under control by firefighters early Sunday.

"All of southwestern Serifos has burned. We are talking about an area where the fire stopped at the sea," Serifos mayor Konstantinos Revintis told MEGA TV.

The fire caused damage to houses, cottages, warehouses and chapels, according to the mayor.

The Fire Danger Forecast Map issued for Sunday by the Civil Protection Ministry predicted a very high category 4 risk of fire for Attica, the Peloponnese, Crete, the North and South Aegean Regions, and central Greece.

A wildfire ignited Saturday afternoon in the area of Mount Parnitha-- known as "the lungs of Athens" -- was controlled Saturday evening with the help of reinforcements from other regions as well as volunteer firefighters.

More than forty wildfires erupted across Saturday in Greece with wind speeds exceeding 100 kilometres (62 miles) per hour, according to fire brigade sources.

Prime Minister Kyriakos Mitsotakis called on Greeks to brace for a difficult wildfire season in his weekly Facebook post on Sunday.

"The difficult times are still ahead of us. Our effort is continuous. In this effort, our allies are new tools that build a new culture of prevention and responsibility," he said.

"The fire in Parnitha was extremely difficult, but it was detected immediately thanks to aerial surveillance with drones that we have implemented this year for the forests and mountainous areas of Attica," he added.