The study, published in the British Medical Journal, examined the mortality levels and concentrations of the tiny particles known as PM10 in the air in 38 large Chinese cities between January 2010 and June 2013.

It found the average PM10 level recorded in these cities during the period was 92.9 micrograms per cubic meter, much higher than the World Health Organization's standard at 20 micrograms.

The researchers, led by Maigeng Zhou at the Beijing-based Chinese Centre for Disease Control and Prevention, said over 350,000 deaths were recorded in the 38 cities in this period.

Based on this, they said China would save three million premature deaths each year if its PM10 level was lowered to the WHO's recommended level.

"This number is likely to be a lower bound estimate of the total number of deaths related to air pollution because the air pollution effect can be larger in rural areas and PM10 is more detrimental to human health in the long run," they said.

"Our findings suggest that adopting and enforcing tighter air quality standards in China will bring about tremendous public health benefits."

PM10, particulate matter produced by traffic and industry, can enter the lungs and bloodstream. Another hazardous airborne particle is the PM2.5, which is smaller and lighter.

China has been waging a war on pollution but its environment minister said last week it still has work to do and needed to get companies and local authorities to toe the line.

Pollution alerts are common in northern China, especially during bitterly cold winters when energy demand, much of it met by coal, rises. (Reporting by Beh Lih Yi @behlihyi, Editing by Ros Russell; Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women's rights, trafficking, property rights, climate change and resilience. Visit news.trust.org)