The South Korean government is warning the public to wear face masks when they go out and is urging the very young and old to stay indoors, in a bid to reduce the impact of the toxic haze that has descended on much of the western part of the country in recent days.

Pollution is a serious problem on the Korean Peninsula during the winter months, with the output from domestic industry worsened dramatically by emissions from vehicles, power plants and industrial facilities that drift on the prevailing winds across the Yellow Sea from China.

That pollution is exacerbated by fine particles of sand from China’s expanding desert regions.

The emergency measures were announced by the Environment Ministry on Wednesday after the hourly average of PM10 fine dust particles reached 50 microgrammes per cubic metre in the air in 12 cities, including Seoul and Incheon and the surrounding Gyeonggi Province.

The move come just days after the World Health Organization warned that 90 per cent of the world's children breathe toxic air every day.

Inhaling the contaminated air can lead to a range of respiratory diseases, asthma and lung cancer and has been linked to birth defects and premature deaths.