With heavy snowfall jamming the roads in Seoul, Singaporean Dominic Phua spent nearly an hour walking home after work.

The 30-year-old marketing director saw a biker zoom by covered in snow, cars skidding even at tortoise pace, and a car stuck between two buses.

"The snow suddenly came and hit so fast and hard," he told The Straits Times yesterday.

"The roads were too slippery and drivers in Seoul were just not prepared, with no winter tyres."

A cold snap has gripped South Korea, with a warning issued for southern island Jeju for the first time in 57 years and overnight snowfall nationwide from Wednesday causing train delays, flight cancellations and minor traffic accidents.

Temperatures in Seoul plunged to minus 16.1 deg C yesterday morning, with a wind chill of minus 25.3 deg C, according to the Korea Meteorological Administration (KMA).

The mercury is expected to drop to as low as minus 20 deg C by tomorrow and is expected to rise above zero only on Tuesday.

The capital's southern Seocho district got the most snow, 13.7cm from Wednesday evening to early yesterday morning.

In the more rural north-eastern Gangwon province, Mount Seorak recorded minus 29.4 deg C.

A cold wave warning was issued nationwide on Wednesday night - the first time in three years.

The KMA said the plummeting mercury is caused by cold air flowing down from near Siberia, but some experts also attributed it to a lower carbon footprint last year, with factories shutting down during the coronavirus pandemic.

Heavy snow continued across the nation yesterday, causing at least 86 flights to be cancelled at Gimpo International Airport, west of the capital. Incheon International Airport also reported seven flights cancelled as at 4pm.

Yesterday morning, traffic was affected, with severe congestion reported. Wary of slippery roads, cars moved at an average speed of 19kmh.

Subway trains were delayed by breakdowns, and some doors were stuck in the freezing cold.

Prime Minister Chung Sye-kyun has issued an emergency order to speed up snow removal work to avoid further traffic disruptions.

More than 8,000 vehicles have been deployed along with some 17,000 people to clear the snow.

The cold wave came as South Korea continues to battle a third surge of Covid-19 infections that has pushed the total number of cases up to 66,686.

The health authorities said the infection curve is finally starting to flatten due to tightened social distancing rules, which includes a ban on social gatherings of more than four people, and aggressive pre-emptive testing.

Wednesday's snowfall was welcomed by many people, who took to social media to post selfies and videos.

Children could be heard laughing as they dashed out to make snowmen or sledge on small slopes in the neighbourhood.

Mr Phua, who has lived in Seoul for five years, said this is the first time that he has witnessed such heavy snowfall in the city.

He decided to walk home as road traffic in the posh district of Gangnam, where he lives and works, was hardly moving.

"Plus the snow was quite a rare sight, so I just wanted to enjoy the walk home," he said.

Along the way, he saw people slipping and falling.

He also saw people pushing vehicles that had stalled in the snow.

"I felt really bad for the people who got stuck trying to get home," he said, adding that some of his friends took up to six hours to get home.

"But it was also quite funny, like when I saw this delivery guy riding a scooter with his whole body covered in snow."