South Korea was blanketed by a yellow dust storm from China, with the fine dust density level hitting a record high this year in almost every part of the nation Wednesday.

As of 5 p.m., the fine dust level in every region in the country was classified as "very bad," which is the worst level.

The Ministry of Environment said Wednesday that it has raised its yellow dust crisis warning, which had been issued to 17 cities and provinces nationwide the previous day, from "attention" to "caution" as of 7 a.m. The raising came 14 hours after the “attention” level was issued for the yellow dust crisis at 5 p.m. on Tuesday.

The dust originated in the Gobi Desert and the Inner Mongolia Plateau on Monday and was brought to Korea by northwesterly winds, the Korea Meteorological Administration explained.

A yellow dust warning is issued "when fine dust warnings are issued due to yellow dust and there is the possibility of a large-scale disaster."

The alert is issued when the average hourly concentration of fine dust particles smaller than 10 micrometers in diameter, known as PM10, exceeds 300 micrograms per cubic meter for two hours.

The Seoul Metropolitan Government issued a warning at 1 a.m. Wednesday. All other cities and provinces across the country had "very bad" dust levels as of 1 p.m. "Very bad" means the daily average concentration of PM10 has exceeded 150 micrograms per cubic meter. As of 5 p.m., the PM10 concentration in Seoul had recorded 271, Gangwon Province 218 and Jeju Island 249.

The Environment Ministry asked related agencies and local governments to share information and respond thoroughly in accordance with the "Yellow Dust Response Manual." The manual covers outdoor activities at schools, requiring outdoor workers to wear masks and carefully monitoring aircraft operations.

The elevated yellow dust levels are expected to continue nationwide through Thursday and ease after rain on Friday.

"As the impact of yellow dust continues in most parts of the country, we ask the public to refrain from outdoor activities as much as possible and pay more attention to personal health care," Environment Minister Han Wha-jin said in a statement.