In southern Italy, after the hottest spring in nearly two centuries, this year's harvest of grapes and other fruit and vegetables is expected to be as much as a month earlier than usual, at the beginning of August.

The heat is "literally cooking" Sicilian lemons on the trees, said farmers' group Coldiretti, while watermelons, peppers, courgettes, peaches and tomatoes are also at risk.

Greece's flora and fauna are suffering and environmentalists warned the sweltering temperatures could have a long-term effect on animal populations and plants.

"Birds, now in their nesting period, laying eggs in exposed nests are at a very high risk," Martin Gaethlich of the Hellenic Society for the Protection of Nature said.

"The eggs are overheating if left uncovered so birds have to remain on the eggs for much longer."

Several other nature groups have also raised the alarm.

Swallows are having problems finding mud for their nests, forcing them to travel further in search for their building material while frogs, toads and salamanders are seeing their habitats dry up, shortening their life span and affecting in turn those animals who feed on them.

"These are all linked to each other. With the frog and toad populations dropping, birds who feed on them have problems finding food as they stay in Greece until the autumn," Gaethlich said.

MILD WINTER

Gaethlich said Greece's unusually mild winter, coupled with a warmer than normal May and the current June heatwave, has already triggered changes that could be here to stay.

Fish stocks in rivers and lakes are dropping as water is pumped out for agricultural use due to a lack of rain, threatening a rare Greek otter which feeds on them.

"Flowers above the treeline on Mount Olympus that start blossoming in May have already competed their cycle, far too early. Among those are several rare, indigenous flowers."

He said a spate of forest fires in recent days triggered by dry weather and high temperatures exacerbated nature's problems.

"This weather creates a web of problems that will have long-term effects if it persists or if it reoccurs in the coming years," Gaethlich said.

In Sicily, fires have spread rapidly in the intense heat in the last few days, have already destroyed thousands of hectares of grain and wheat crops.

In Turkey, two boys trying to cool down in a small lake in Sakarya province near Istanbul drowned on Wednesday, the private NTV television channel said.

A drought in southeast Europe has already threatened grain crops in countries including Bulgaria, Romania and Turkey, where the Anatolian news agency quoted the head of a big cooperative as predicting a 50 percent drop in this year's cotton crop.

As Greeks turned up air conditioners, parts of the country were hit by power outages and the state power utility was forced to import extra power from neighbouring states.