In China, pedestrians used any protection

The dust storm was first reported in China's capital Beijing on Wednesday. State-controlled media said it was the worst in a decade and affected 100 million people across the country's north.

It is being blamed on arid weather, the ploughing up of pasture land for agriculture and prevailing winds.

Dust storms affect the region each year, though a severe summer drought in northern China has made this year's problem worse.

In Seoul, people rushed for cover using handkerchiefs and masks to shield their faces.

Primary schools and kindergartens in the capital and central west-coast provinces were closed, though they were expected to reopen on Saturday.

About 35 domestic flights were cancelled, after 70 had to be called off on Thursday.

Environmental fears

China's government has vowed to try and deal with the problem.

The Chinese capital Beijing is now less than 250-kilometres from the encroaching desert, prompting alarm from officials and from the public.

Experts have warned that sandstorms could be a major problem for Beijing when it hosts the 2008 Olympics.

The government has pledged $6.8bn (56.8bn Yuan) on an environmental programme which includes planting a green belt of trees around the capital.