The Greek power utility urged the residents of the country to reduce energy consumption over the next two days in order to avert a possible blackout.
As temperatures rose to 38 degrees Celsius (100.4 Fahrenheit), the Public Power Corporation said households should avoid excessive use of air-conditioners, washing machines and other appliances that require a lot of energy during the hottest time of day.
"Particular care should be shown today and tomorrow, when high temperatures are forecast," the power company said. It added that its customers should continue to show restraint on hot days throughout August, between 11 a.m. and 3 p.m (0800 and 1200GMT).
To ensure unhindered power supply for major cities, the power utility carried out selective cuts in power for irrigation in agricultural areas.
The country's power distribution system was overhauled following a major blackout that hit Athens and much of southern Greece in July 2004 - just a month before the opening of the Olympic Games, the AP reports.