At least 150 houses were destroyed by a violent blaze that surrounded a monastery and a dozen villages on the Greek island of Evia on Wednesday, just one of some 40 fires raging in the heatwave-hit country.

Firefighters were also battling a blaze near Athens, while flames threatened Olympia, the birthplace of the Olympic Games where the mayor pleaded for back-up.

On Evia, huge flames leapt up from the forest, visible from afar in what firefighters said was a difficult blaze to control on an island of rolling hills with little visibility.

Three monks from Saint David Monastery had refused to leave, firefighters said, adding that everyone else had been evacuated from the villages nearby.

"The flames are 30 to 40 metres (100 to 130 feet) high and surrounding the monastery. We're suffocating due to the smoke," one of the monks told the ANA news agency by phone.