BRITS heading to Greece have been warned of an "insidious" heatwave with the mercury set to hit a sizzling 45C in some regions.

       The first heatwave of the summer is due to last ten days with temperatures reaching an average of 42C to 43C across the country.

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       Greece's first heatwave this summer is set to start this week Credit: Getty 2

       Temperatures on Friday are set to reach 45C Credit: meteo.gov.gr

       Forecasters predict the heatwave is set to start on Wednesday and is expected to peak up to 45C on Friday.

       The director of Greece's meteorological agency, Thodoris Kolidas, said the heatwave will have a long duration and possibly last until the beginning of next week.

       He described the heatwave as "insidious and dangerous" - and noted it will be particularly hot in the evenings with temperatures above 30C.

       Greece's National Meteorological Service has issued an emergency bulletin of dangerous weather phenomena.

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       It states the heatwave CLEON is expected to last at least six days the highest temperatures being on Friday and Saturday as the mercury is expected to reach up to 45C in some cities on the mainland and 39C to 40C in the islands.

       The regions of Thessaly, northern Greece and Peloponnese are expected to see highs of 45C, with 42C in Rhodes, Crete and Athens and 39C to 40C in the rest of the islands.

       Forecaster Giannis Kallianos warned that strong winds on Sunday will cause the temperature to drop from 38C to 39C - but will also trigger an alert for wildfires.

       On Monday the temperature is set to rise again.

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       Meteorologist George Tsatrafillias said: "There are three elements that concern me regarding the upcoming African heat wave.

       "It's aggression on Friday and Saturday. Temperatures may exceed 44 degrees in heat-sensitive areas."

       Even at night, the temperature will be around 30C in the cities, the forecaster added.

       He said the dry and warm conditions are particularly concerning as they increase the possibility of wildfires.