South Korea issued a warning for a possible power shortage Friday as high temperatures led to a large increase in power consumption for cooling.

Friday's warning was the second of its kind issued this year.

The preliminary warning was issued at 1:39 p.m. after the country's power reserves dipped to below 3.5 million kilowatts, the Korea Electric Power Corp. said in a released statement.

A light warning is issued when the power reserves fall below 4.5 million kilowatts, followed by a preliminary warning when the power reserves dip to below what is considered a safe level of 3.5 million kilowatts.

A near depletion of the power reserves in September 2011 caused a massive blackout that affected some 3.5 million households throughout the country.

The country's power supply experienced a significant setback earlier in the year when it was forced to shut down two operational nuclear reactors, each generating 1 million kilowatts of electricity, for their substandard parts provided under fabricated quality certificates in 2010.

As many as seven other reactors out of the total 23 in the country had also been shut down at the same time for scheduled maintenance or inspection.

Three of the reactors have been put back to work, but a month-long heat wave that hit parts of the country is now causing troubles for the government and state power providers struggling daily to prevent a nationwide blackout.

As of 1 p.m. Friday, the mercury stayed well above 36 C in Daegu, 300 kilometers south of Seoul, with temperatures in southeastern port city of Ulsan reaching 37 C, according to the Korea Meteorological Administration. (Yonhap News)