The governments of Seoul and Gyeonggi Province on Friday issued their first ultrafine dust advisories this year, urging people to stay indoors.

In Seoul, the advisory was put in place at 11 a.m. after the city's atmospheric concentration levels of "particulate matter 2.5" pollutants stood around 95 micrograms per cubic meter for more than two hours. It was the year's first advisory of its kind issued by the Seoul metropolitan government.

The Gyeonggi provincial government posted the same advisory for 11 cities, including Seongnam, Bucheon, Ansan, Anyang and Siheung, at 10 a.m. when levels of PM-2.5 reached up to 145 micrograms per cubic meter in those regions.

The advisory was the first ever issued by the province since the advisory system was put in place at the start of the year.

Seoul's level of PM-10, better known as fine dust, is also rising.

The average PM-10 concentration per hour fell to 137 micrograms per cubic meter at 7 a.m. after peaking at 190 micrograms per cubic meter at 2 a.m. But it has since been getting thicker, reaching 188 micrograms per cubic meter at 11 a.m.

An official at the Korea Meteorological Administration said stagnant air as well as fog caused the unhealthy pollution levels.

"Dust particles are not likely to be scattered easily because winds are not that strong," the official added.

All 20 flights scheduled to leave Gimpo Airport in Seoul at 10:30 a.m. for provincial areas were canceled due to poor visibility caused by fog and dust.

The ice rink in front of Seoul City Hall also was closed for the morning. (Yonhap News)