China is registering record levels of air pollution as an early onset of winter has led the authorities to turn on central heating, which is generally powered by coal.
The provinces of Jilin and Liaoning have been worst-affected, where PM2.5 (poisonous tiny airborne particles) levels have exceeded 1,000 mg per cubic metre, official data revealed on Monday.
The levels are the worst recorded in the country so far, EFE news reported.
Although PM2.5 levels of 25 mg per cubic metre is deemed safe by the World Health Organisation, 849 mg was recorded on Monday morning in Changshun, capital of Jilin province, while in Jilin city it was 776 mg.
Local authorities urged residents to remain indoors and called upon the factories to reduce production, as emissions from factories and vehicles are among the major causes of air pollution.
Coal continues to be the major source of energy in China, while the authorities are attempting to make a shift towards cleaner sources of energy.
For example, the government has been shutting down coal plants in Beijing and other cities and promoting natural gas instead.