Residents of China's capital, Beijing, have been warned to take precautions after air pollution readings soared.

Readings on Thursday registered more than 20 times the recommended exposure levels by the World Health Organisation (WHO).

Thick smog reduced visibility to a few hundred metres, shrouding skyscrapers and leaving an acrid smell in the air.

Officials advised people going to work to wear protective masks, and children and the elderly to stay indoors.

Beijing is often hit by thick smog caused by air pollution

WHO guidelines say average concentrations of the tiniest pollution particles - called PM2.5 - should be no more than 25 microgrammes per cubic metre.

On Thursday, official readings for PM2.5 at one point showed more than 500 microgrammes per cubic metre.

Another monitoring post at the US embassy said the pollution level was briefly more than 25 times higher than the amount considered safe by WHO.

Four highways linking Beijing to other cities were temporarily closed on Thursday morning due to poor visibility, Xinhua news agency says.

(Source: BBC)