South Korea's weather service Friday issued a warning against airborne pollution known as "yellow dust", advising residents in western areas to avoid outdoor activities.
"Yellow dust which originated in Mongolia reached South Korea, blanketing most of the western parts of the country," the National Meteorological Administration said in a statement.
"As the effect of the dust storm can spread to the nation, it is desirable to refrain from outdoor activities."
The warning covered the capital Seoul and adjacent areas as well as South Chungcheong and Jeolla provinces.
Weather officials quoted by Yonhap news agency said it was the first time yellow dust had been spotted on Christmas Day in South Korea. The dust storms usually hit the country in spring.
Yellow dust -- fine sand blown from China and Mongolia which sometimes includes toxic chemical smog emitted by Chinese factories -- can cause respiratory disorders.
South Korea is helping to fund tree-planting projects in China to control the phenomenon.
Explore further: Changes in forest structure affect bees and other pollinators