More coal was burnt this winter as weather conditions were more severe than usual.

In addition, Zhang said, neighboring cities have also contributed to the capital's pollution.

Shijiazhuang topped the list of cities for the worst air pollution on Saturday.

A cold front is forecast for the capital on Tuesday and this will result in cleaner air from Wednesday.

Experts say the pollution and measures to reduce it have already hit the economy.

Officials at Monday's news conference declined to speculate on the financial repercussions of the smog.

However, Feng Yongfeng, founder of Green Beagle, an environmental protection NGO in the capital, said the emergency measures "will definitely set back construction on many projects". Although, he added, "it might be time for the city to slow down''.

Zhang Hui, a professor of tourism from Beijing Jiaotong University, said the city's tourism will also be affected, as conditions put off visitors and residents from seeing the sights. "People will not venture out if it is unhealthy. This applies to city residents and to potential visitors.''

The Ministry of Environmental Protection called on Monday on regional environmental departments to improve monitoring of air quality and warn the public of haze hazards by analyzing weather patterns and issuing forecasts.

Wu Wencong contributed to this story.

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Air quality suffers due to smog