China has issued a smog "red alert" for large parts of the country, urging for schools to be closed, cars to be restricted and residents to stay indoors. The alert is expected to begin Saturday and last until Tuesday.

Beijing lifted the previous "red alert" on December 10 when northern winds dispersed the polluted air, which has been largely blamed on coal power plants, vehicle emissions and factory operations.

The National Meteorological Centre said the wave of smog would cover large parts of central China and stretch across to the northeast area of Harbin, with Beijing's 22.5 million residents expected to be caught in the middle.

Forecasters have predicted that levels of PM2.5 - the deadliest form of particulate matter - will exceed 500, which is more than 20 times the World Health Organization's recommend level.

According to China's government guidelines, a "red alert" is triggered when the index passes 200, and people are cautioned to stay indoors when the index exceeds 300. The red alert is the highest tier of a four-color warning system.

Visibility is also expected to be very minimal in the most affected areas, which will most likely include Beijing.

Drastic changes needed

China is the world's biggest carbon emitter, and has said it plans to upgrade coal power plants over the next five years as part of its climate change obligations.

Germany's Max Planck Institute published a study in "Nature" magazine estimating that some 1.4 million people die prematurely in China each year because of the effects of pollution.

smm/jm (dpa, Reuters)