Wildfires raged Saturday on Spain's Canary Islands, as hundreds of firefighters also battled a blaze near Greece's Mount Athos, a World Heritage site housing an ancient monastic community.

Hundreds of hectares were in flames in Spain as a pitiless heatwave showed no signs of relenting after the most devastating fires of the decade had been nearly tamed before re-erupting on La Gomera in the Canaries.

Forest fires that broke out a week ago have already ravaged some 3,000 hectares (7,400 acres) of land on La Gomera, including about one-tenth of the Garajonay nature reserve, also a UNESCO World Heritage site.

The fires on La Gomera and Tenerife islands have forced the evacuation of more than 4,700 people in two days, the regional government said.

Firefighters battling the blazes on the islands off Morocco were up against "high temperatures, low humidity and wind" that fanned the flames, said regional economy minister Javier Gonzalez Ortiz.

"The fires are still burning on three fronts," an emergency services spokesman said earlier. "There is no positive change for the moment."

Water-dropping aircraft flew missions as blazes erupted anew in Garajonay, home to rare subtropical forests, which covered the Mediterranean region tens of millions of years ago but have now largely disappeared.

It also boasts 450 plant species, including eight found only in the park.

Ventura del Carmen Rodriguez, Gomera island's environment secretary, said last week it would take 30-40 years for Garajonay's burned areas to recover.

Three more villages were evacuated after 300 people fled their homes on Friday, as roads leading to the affected areas were cut off.

Restaurateur Victor Manuel Garcia, 40, said he was among a handful of residents in his village, Chipude, to stay put. "There's not as much black smoke," he said. "It's hot but there is less wind."

Chipude was evacuated for the first time last week and again on Friday, but Garcia said "someone had to stay in case of an emergency."

He had expected his 40-seat restaurant to fill up with tourists attending a village fete beginning Sunday, but that had to be cancelled.

Meanwhile on the Spanish mainland in northwestern Galicia, two villages in Ourense province were evacuated Friday as flames devoured another 800 hectares of vegetation, the regional government said.

Another wildfire erupted Saturday in Spain's Gers region bordering France, devastating 200 hectares of forest, officials said, adding that French firemen were helping their Spanish counterparts check the flames.

Spain has been battling fires both in the Canaries, which are off the Moroccan coast, and on the mainland after a winter that saw almost no rainfall, leaving the landscape its driest in seven decades.

In Greece, hundreds of Greek and Serbian firefighters battled a wildfire ravaging a forest near the remote Mount Athos in the country's north-east.

The region houses some 20 Eastern Orthodox monasteries which are self-governing and date back more than 1,000 years to Byzantine times. Mount Athos treasures its isolation and is only accessible by boat.

Two hundred Greek firefighters backed by about 50 sent from neighbouring Serbia as well as 120 volunteers fought the fire.

The Greek army dispatched more than 300 soldiers and 50 vehicles to join the effort. Fourteen water-bombing planes and seven helicopters were also doing rotations.

The fire erupted Saturday near the Serbian monastery of Hilandariou, or Chelandari, at Mount Athos, in a forest untouched for decades.

The fire was raging Saturday afternoon but did not threaten any of the monasteries. Strong winds, which frequently changed direction, were making firefighting efforts difficult, a spokesman said.

The blaze, which may be the result of arson or negligence, had destroyed 1,500 hectares (3,700 acres) of forest and consumed olive trees and vines.

Greece is reeling under temperatures of 40 degrees Celsius (104 Fahrenheit) to add to its economic woes.