Cold air from the North Pole gripped the nation on Friday, pushing the mercury down to minus 29.1 degrees Celsius on a mountain peak in Gangwon Province and minus 21.7 degrees in northwestern Seoul.

The capital’s official overnight low, measured in Jongno-gu, hit minus 18.6 degrees, the lowest since Jan. 5, 1986.

In Gangwon Province, the cold spell froze the Soyang River and Bukhan River in Chuncheon, as well as a waterfall on the Hantan River in Cheorwon. Seawater icicles even formed on rocks on the shores of Sokcho.

Overnight lows marked minus 29.1 degrees on Hyangnobong, minus 28.6 degrees on Seoraksan, minus 21.8 degrees in Chuncheon, minus 17.8 degrees in Wonju and minus 15.1 degrees in Gangneung.

Due to strong winds, it would have felt even colder -- minus 44.1 degrees on Hyangnobong at one point and minus 27.4 degrees in Chuncheon.

Cold wave advisories have been issued for the eastern coastal towns, while cold warnings have been issued for all the remaining 13 townships and counties in Gangwon Province.

Daily highs are forecast to range between minus 12 and minus 9 degrees in the inland areas of the province, between minus 15 and minus 12 degrees in the mountainous regions, and between minus 9 and minus 5 degrees on the east coast.

The mercury also dropped below minus 20 degrees in the central inland regions, the eastern part of North Jeolla Province and the northern inland area of North Gyeongsang Province; and below minus 15 degrees in other parts of the country’s central region, in the western part of North Jeolla Province, the northern part of South Jeolla Province, other parts of North Gyeongsang Province and western inland areas of South Gyeongsang Province.

The Korea Meteorological Agency said temperatures would rise slightly on Saturday as the inflow of cold air from the north weakened, but the cold spell would continue for a while.

It will continue to snow through Sunday in some parts of the Jeolla provinces, and on the islands of Jeju, Ulleongdo and Dokdo.

The KMA advised outdoor workers such as those at COVID-19 screening centers to take extra caution, along with senior citizens and people with health problems. It called for high vigilance as water pipes may freeze and burst, and vinyl greenhouses and fish farms could suffer damage.

The weather agency also advised caution to ensure traffic and pedestrian safety as frozen snow in the inland areas would make roads and sidewalks slippery, and it would be difficult to walk up and down hills, slopes and shaded backroads.

By Kim So-hyun (sophie@heraldcorp.com)