Ultrafine dust plagued most parts of South Korea on Saturday, prompting authorities to take emergency emissions reduction measures against bad air quality, according to officials.

According to the National Institute of Environmental Research, the level of ultrafine dust in the greater Seoul area, Chungcheong and North Jeolla regions were all recorded at "very bad" on Saturday morning.

South Korea measures air pollution in a four-tier system -- "good," "average," "bad" and "very bad."

The institute predicted the air quality to remain at the "bad" level except in the southern island of Jeju due to air stagnation.

Amid the spike in fine dust levels, authorities ordered emergency emissions reduction measures in the greater Seoul area, Sejong city, South Chuncheong Province and North Jeolla Province.

Weather authorities expect the air quality to remain poor in many areas until Monday. (Yonhap)