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Greek firefighters backed by water-dropping planes and helicopters were battling a wildfire burning through a protected nature reserve on the island of Evia for a second day Wednesday, where hundreds of people had been evacuated from four villages and a monastery.

The six planes and five helicopters were concentrating on areas where access to the island's dense pine forest, which includes canyons, was difficult by land. More than 250 firefighters, dozens of soldiers and volunteers were battling the wildfire that broke out at 3 a.m. Tuesday.

A state of emergency was declared for the area on Tuesday, when strong winds had hampered firefighting and carried smoke from Greece's second-largest island as far as the capital, Athens, 75 kilometres south.

The winds died down somewhat Wednesday and authorities expressed cautious optimism about the progression of the fire, although it had still not been brought under control.

"Things are better, but ... no complacency is allowed and I would ask everyone to carefully follow the orders and directions of the civil protection authority and the fire department," Prime Minister Kyriakos Mitsotakis said during a visit to the area.

Authorities said around 28 square kilometres had been burnt by mid-day Wednesday. One volunteer firefighter who suffered burns remained hospitalized Wednesday.

Thanking firefighters for their efforts, Mitsotakis said "drastic interventions" would be made in the way that civil protection operates.

"I am satisfied by the level of co-ordination but there is still other work that needs to be done," he said. "We know that wildfires will be with us. They will be part, as they have always been, of our daily life as climate change is taking its toll on southern Europe."

Vasilis Pirgos, a villager from Kontodespoti, one of the four villages evacuated Tuesday, said they had "tried with every means we had to control the fire and for it not to enter the village and burn the houses. Thankfully we had support from the air. We had many helicopters over the village dropping water continuously and we managed to save the houses."