Sirens rang out across South Korea and some traffic lights were switched off Thursday as the country carried out an unprecedented drill aimed at averting summer power cuts.

The 20-minute exercise was intended to encourage consumers to switch off appliances if reserves run dangerously low, and to simulate responses if phased blackouts become inevitable, the ministry of knowledge economy said.

Reserves are feared to fall to dangerously low levels in July and August when air conditioners will run at full blast, a situation that could spark rolling blackouts across the country as on one day in September last year.

Traffic lights were turned off at 17 intersections nationwide, state KBS TV reported. At a busy intersection outside Seoul City Hall policemen wielding glowing batons struggled to control heavy traffic.

At four subway stations in Seoul, firemen simulated operations to rescue passengers trapped in elevators. Some large hospitals evacuated patients from emergency rooms.

Government buildings cut off mains power and switched on generators.

People were urged voluntarily to switch off air conditioners and fans and stop using irons, vacuum cleaners, washing machines and electric ovens during the drills.

Shops and private buildings were encouraged to pull the plug on their air conditioners, computers, coffee pots and vending machines.

Factories were asked to cut energy consumption during the exercise as much as possible without disrupting production.

"I wasn't really sure what to do when the sirens went off, but I vaguely knew it was an energy drill," said Jeong Woo-Jae, 26.

"I think such drills are necessary, but feel it wasn't advertised enough to the public."

Experts point to air conditioners and home appliances for pushing up electricity demand.

Power shortages are expected to continue until 2014 when new power plants come on stream, a knowledge economy ministry official told YTN TV.

Construction of the new plants has suffered long delays due to protests by residents living near the sites.

Both North and South Korea have also experienced a long drought and an unusual heat wave in the past several weeks. Power reserves earlier this month fell to a dangerously low level in the South.

The drought has ravaged crops in the North, triggering fears that persistent food shortages will worsen.