Fires have been raging through a "unique, untouched pine forest" on the Greek island of Evia as authorities fight to keep the flames under control.
Hundreds of people were evacuated from nearby villages as the fire broke out in the early hours of Tuesday and ravaged through the dense forest.
"It's a huge ecological disaster," acting regional governor Kostas Bakoyannis told AFP.
More than 200 firefighters are helping to combat the blaze along with 75 fire engines, nine helicopters and seven planes, the news agency reports.
Italy and Spain have offered additional aircraft to help dump water on the forests in an attempt to douse the flames burning through Greece's second-largest island.
Other wildfires broke out on the island of Thassos as well as in the central region of Viotia and the Peloponnese. There was also a fire reported in Peania, a suburb of Athens.
Smoke has blanketed the Greek capital of Athens, 110 km (70 miles) away from the island.
The fire broke out after a weekend that saw temperatures soaring near 40C (104F) with strong winds.
Newly-elected Prime Minister Kyriakos Mitsotakis cancelled his summer holiday plans and acknowledged that firefighters had "given their all" to tackle the flames, often with little sleep and food.
The regional governor, Costas Bakoyannis, told Skai TV the situation seemed to be improving after "superhuman efforts" to control the flames on Tuesday night.
The European Union's humanitarian commissioner, Christos Stylianides, said it "remains difficult", but suggested they might be able to "to limit the ecological losses".
Greece was devastated by wildfires in 2018 that tore through pine forests surrounding Athens, leaving 100 people dead.