The reserve power level fell to 7.1 percent at 3 p.m. on Wednesday as unseasonable heat hit the country. As peak demand soared to 59.19 million kW, only 4.22 million kW of reserve power remains.

The reserve power level shows how much electricity can be supplied in addition to the current usage. This is the first time this year it fell below 4 million kW, apparently because of a sudden rise in the use of air conditioners.

Concerns are growing over the country's capacity to supply electricity this summer now that red lights are flashing even before the summer is in full swing. The electricity authority normally maintains the reserve power level at 5 million kW to secure stable supply.