Authorities in Beijing, have issued their highest smog warning so far this year, BBC News reported.
The “orange level” alert declared on Sunday is the second-highest possible, requiring factories to cut or shut down production.
On Sunday, some pollution readings in parts of the city reached about 17 times the maximum considered safe by the World Health Organisation.
Building sites are not allowed to transport materials or waste, and heavy-duty trucks are banned from the city’s roads.
Some reports suggest visibility has fallen to a few hundred meters in some places.
At noon on Sunday, the air pollution monitor operated by the US Embassy in Beijing reported that the intensity of the poisonous, tiny PM 2.5 particles reached more than 400 micrograms per cubic meter in some of the worst-affected areas.
The World Health Organization considers 25 mcg per cubic metre to be a safe level.
Coal-powered industries and heating systems, as well as dust from construction sites, contribute to the smog, which has been exacerbated by humidity and a lack of wind.
Earlier this year China’s environment ministry announced that only eight out of the country’s 74 biggest cities had passed the government’s basic air quality standards in 2014.
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