The entire country was on alert on Thursday as toxic haze from China was blown into the Korean Peninsula.

The National Institute of Environmental Research said that the concentration of fine particles would stay at the mildly dangerous level of 81-120 ㎍/㎥ on average across the country from Thursday until Friday morning and advised old or weak people and patients with respiratory diseases to avoid staying outdoors.

The Seoul Metropolitan Government also issued a preliminary warning on Thursday afternoon. It said the haze was blown in on westerly winds, blanketing Baeknyeong Island, the westernmost island, and then Seoul.