SEOUL - Under hazy spring sunshine on Saturday, hundreds of young Seoulites turned up at a park by the Han River at the invitation of the city government to try to do something many overworked South Koreans never get enough of - sleep.

The Seoul Metropolitan Government staged its third annual spring event, dubbed a power nap contest, from 3 p.m. (0600 GMT), under a refreshed set of admission requirements for would-be participants: wear outfits befitting either a sleeping beauty or prince, come tired, with a full belly.

For a metropolis that famously runs on 24-hour shopping malls, competitive hustle and iced Americanos, the underlying exhaustion on the lawn was palpable.

"Between exam prep and part-time jobs, I survive on three or four hours of sleep a night, patching it up with desk naps during the day," said Park Jun-seok, who showed up draped in the silken, crimson robes of a Joseon Dynasty monarch.

"I'm here to show off my napping skills, and to demonstrate exactly how a king sleeps," said Park, a 20-year-old university student.

Nearby, Yoo Mi-yeon, 24, an English teacher from Ilsan north of Seoul, stood out in a plush, oversized koala-themed onesie.

"I've always suffered from insomnia, I struggle to fall asleep, and wake up easily," she said. "Koalas are famous for their deep slumber. I came dressed as one hoping to borrow a little of their magic."

Now in its third consecutive year, the sleep competition underscores a chronic issue for South Koreans.Data show South Korea is one of the most overworked and sleep-deprived nations among Organisation for Economic Co-operation and Development members, and, as a consequence, people have some of the fewest sleep hours.

As the clock struck three and eye masks descended across the park, officials went around to measure participants' heart rate to make sure they had a stable reading - an indicator of deep, peaceful sleep.

The winner of the contest was a man in his 80s.

Hwang Du-seong, a 37-year-old office worker, was a runner-up.

"I was completely drained, having done night shifts often on top of going to work everyday plus I also drive a lot for work. So when I saw the contest I was determined to sleep to fully recharge amid river breeze, and I'm very happy to be placed second place, luckily."

-Writing by Cynthia Kim; Editing by Sharon Singleton/Reuters