Hundreds of Greek firefighters were battling a huge blaze on Monday that has killed at least 20 people over the past 10 days, Europe's deadliest wildfire so far this summer as record-setting heatwaves unleash blazes across the continent.

The fire, which began near the city of Alexandroupolis, has raged uncontrolled in northeastern Greece's Evros region, turbocharged by near-gale force winds and high temperatures. All but one of the victims killed so far were irregular migrants hiding in the forest.

"It is the definition of what we call a megafire," government spokesman Pavlos Marinakis told a regular briefing.

The European Union-backed Copernicus Climate Change Service said the Evros blaze had burned more than 77,000 hectares of land, making it one of the biggest on European soil in years.

"We tried to wet the land with hoses a bit, for protection, but the water was evaporating in no time," says 40-year-old beekeeper Michalis Tsolakis, who lost 350 beehives in the village of Kirki, in Evros region. "Ιt just wasn't possible to save anything."

Marinakis said the country's climate crisis and civil protection minister and other senior government ministers had visited the area to assess the damage.

Lawmakers were expected to discuss the impact of the devastating fires and state preparedness in parliament on Thursday. Firefighting forces from Cyprus, Germany, Sweden, Bulgaria and Slovakia have been assisting Greece's efforts to put out the blazes in recent weeks.

Meanwhile, a wildfire on the outskirts of Athens that began last Tuesday had abated, the fire brigade said. Scores of people have had to flee their homes across Greece as hundreds of wildfires erupted across the country in the second major fire outbreak of this summer.

In July, some 20,000 foreign tourists were evacuated from the island of Rhodes, where a wildfire burned resorts and hotels. (Reuters)