State-run Korea Electric Power Corp. is facing mounting criticism as it passed the buck to the Korea Power Exchange on taking responsibility for the unprecedented nationwide power outages Thursday afternoon.

Residents and workers around the country suffered sudden power outages starting at around 3 p.m. as a heat wave pushed up electricity demand beyond capacity.

The KPX cited a drop in its electricity reserves as the main cause of the blackouts due to a temporary shutdown of some power generators as part of its post-peak maintenance plan.

But KEPCO, Korea’s sole electricity provider, simply referred all inquiries to the KPX, saying the energy-trading exchange is “in charge of coordinating electricity flows according to supply and demand in the market.”

Even though the state-run utility released a statement later in the evening following a rash of news reports, many residents and critics were furious with the slack responses.

“I had to return home in the middle of paying bills at a bank because power, air conditioners and tellers’ computers all went out,” a Seoul resident said on Twitter.

“If it really had expected low supplies and brownouts, KEPCO should have notified us of it beforehand,” another Twitter user posted.

Despite no injuries, the incident crippled business operations in the financial district of Yeouido and other parts of Seoul and production lines in the country’s southern regions. Major energy-intensive manufacturers such as Samsung Electronics, Hyundai Motor Group and POSCO weathered shortages but small- and medium-scale factories were hit hard.

The Ministry of Knowledge Economy appeared unlikely to escape from escalating criticism as it has long been preparing for a demand spike, which has often caused serious electricity cuts in the past.

Last week, it even touted its “successful” preparations for the peak period, saying its “preemptive measures and policies enabled the country to get through the summer without any crisis.”

Critics also pointed out that Thursday’s maximum demand of 67.26 million kilowatts was not even closer to the previous high on August 31, which stand at 72.19 million kilowatts.

The Korea Meteorological Administration had also forecast a heat wave after the Chuseok holidays, which ended Tuesday.

By Shin Hyon-hee (heeshin@heraldcorp.com)