Thousands of people fled their homes on the outskirts of Athens on Friday as emergency crews struggled to stop wildfires from spreading to more towns while scorching winds fueled blazes across Greece for the fourth day.

Like elsewhere in Europe, Greece has been grappling with extreme weather this summer and a week-long heatwave - its worst in 30 years - has sparked simultaneous wildfires in many parts of the country, burning homes and killing animals as flames tear through thousands of acres of land.

There were 56 active fronts across Greece on Friday, from the Peloponnese to the island of Evia near the capital, where hundreds of people had to be evacuated by boat as flames burned through forestland to the shore.

"We are continuing our efforts, hour by hour, to tackle multiple fires today," Deputy Civil Protection Minister Nikos Hardalias said, as authorities ordered the evacuation of more suburbs north of Athens, where wildfires on the foothills of Mount Parnitha burst back into life late on Thursday.

"Conditions are extremely dangerous," he said.

The fire, which first broke out on Tuesday, burned around the main highway linking the capital to northern Greece and hundreds of firefighters with water-bombing aircraft were engaged in a "titanic effort" to prevent the flames reaching the nearby town of Marathon, Hardalias said.

"We might have to spend the night in the car if we don't find a friend to host us," said Yorgos, 26, who had to leave his home in the suburb of Polydendri.

In neighbouring Turkey, authorities are battling the country's worst ever wildfires, and flames sweeping through its southwestern coastal regions forced the evacuation of tens of thousands of people. In Italy, hot winds fanned flames on the island of Sicily this week.

'A CATASTROPHE'

Athenians were told to stay indoors again to avoid toxic fumes as the blaze, fuelled by winds and explosions on high-voltage power lines, sent a cloud of smoke over the capital.

Temperatures have been over 40 degrees Celsius (107 Fahrenheit) all week and no let up was expected on Friday with gale force winds expected to spread the flames further.

The Athens power grid operator announced staggered power cuts in the surrounding region to ensure there were no major outages in mainland Greece.

On Evia, coastguard vessels assisted by tourist boats have picked up 631 people since late Thursday from three beaches on the island, where the flames have burned through a vast area of pine forest since Tuesday and reached the sea.

The island's deputy governor, George Kelaiditis, called it "the biggest catastrophe in Evia in 50 years," with hundreds of damaged houses and thousands of acres of burned forest land.

In the Peloponnese, where firefighters saved Ancient Olympia, the site of the first Olympic Games, from a raging fire this week, the flames left behind scorched earth and dead animals.

"A catastrophe," said farmer Marinos Anastopoulos. "The fire came around midday with swirling winds and homes were burned, a lot of animals burned to death. Rabbits, sheep, dogs, everything."

Joining firefighters from countries including France, Cyprus and Sweden, Israel said it was sending a team of 16 firefighters to Greece.