Beijing marathon runners don face masks to battle severe smog

About 30,000 runners - some donning gas masks - took part in an international marathon in Beijing yesterday, braving the choking smog that again blanketed the capital.

The government issued a blue warning for air pollution - meaning the air quality was unsuitable for outdoor activities. There has been controversy over whether the organisers should have postponed the event as the haze was forecast days ago.

The smog also blanketed other northern cities in Hebei , Shandong and Henan provinces, as well as Tianjin , with the National Meteorological Centre issuing a yellow warning for haze. Pollution readings in Dingzhou , in the southwest of Hebei, went beyond the highest level on the index.

Watch: Beijing Marathon runners brave hazardous air pollution

Late on Saturday, organisers of the marathon warned competitors that there would be "slight or moderate smog" on race day, and asked runners to take precautions based on their own health conditions, advising the elderly and people with respiratory diseases to carefully consider whether to participate.

Beijing's official Air Quality Index, however, climbed above 400 early yesterday morning - showing the pollution was at "hazardous" level and that all groups of people should avoid outdoor activities - when runners started the race at Tiananmen Square.