SEOUL, Jan. 14 (Xinhua) -- South Korea's sky was blanketed thick with ultrafine dust for four straight days on Monday, prompting the government to take emergency measures.

According to Air Korea of the quasi-government Korea Environment Corp., the fine dust concentration of the capital Seoul stood at 189 micrograms per cubic meter as of 1:00 p.m. local time (0400 GMT).

The capital city's ultrafine dust level was 147 micrograms, far surpassing 25 micrograms recommended by the World Health Organization (WHO).

The level of fine dust above 80 is classified as "bad," and above 150 as "very bad." The level of ultrafine dust, smaller than 2.5 micrometers in diameter, above 35 is categorized as "bad," and above 75 as "very bad."

The ultrafine dust was serious especially in the country's northern and central region. The fine dust level of Gyeonggi province, surrounding Seoul, came in at 183 micrograms, with its ultrafine dust level surging to 142 micrograms.

The severity of the ultrafine particle continued for the fourth consecutive day as chilly northern winds gave way to warm eastern winds.

The fine dust level was forecast to fall from Tuesday afternoon when temperature is expected to be brought down by cold winds blowing away the fine dust.

To fight fine dust, the environment ministry ordered thermal power plants to reduce their operation to 80 percent of normal ones.

The Seoul metropolitan government banned half of vehicles from the road for the second consecutive day. It was the third time after January and March last year that the Seoul government took such measures.