China said Friday that two-thirds of its cities currently fail to meet new air-quality standards introduced this week that are based on the pollutants most harmful to health.

Under pressure from a worried Chinese public, the government this week issued revised air-quality targets based on the smallest particulates, which make up much of the country's air pollution.

Cities will have four years to get their pollution levels down to the new limits, which cover levels of ozone and particulates measuring 2.5 micrometres or less, known as PM 2.5.

The new standards are in line with the World Health Organisation's recommendations for lowering pollution in developing countries, but are more than three times higher than the body's internationally recommended goals.

"After the new standard is implemented, two-thirds of our nation's cities will not meet the air quality requirements," Wu Xiaoqing, vice minister of environmental protection, told a news conference in Beijing.

"This shows we are facing a more serious challenge."

Wu said the new requirements would be implemented nationwide by 2016 as China seeks to control the sources of particulates, such as coal burning and auto emissions.

International organisations say a doubling of coal consumption over the last decade and booming auto sales that have made China the world's biggest car market have made its air quality among the worst in the world.

The new limits come after authorities in Beijing this year bowed to a vocal online campaign for a change in the way air quality is measured and pledged to start publishing figures showing PM 2.5.

The Chinese capital previously based its air quality information on particles of 10 micrometres or larger, and regularly ranked the city's pollution levels as low, even when a thick smog could be seen.

Public anger was exacerbated by the discrepancy between the official data and that issued online and on Twitter by the US embassy in Beijing, which conducts its own measures of PM 2.5.

Environmental group Greenpeace, speaking Wednesday after the new standard was unveiled, urged China to put limits on coal use.

"Not only must cities let their people know about the air they breathe every day, they must also start addressing air pollution by controlling pollutants discharged into the air," Greenpeace said in a statement.