Beijing is to unveil unprecedented new rules against hazardous air pollution in China's capital, as deteriorating air quality threatens to become a rallying point for wider political dissatisfaction.

The rules will formalise previous ad-hoc measures, including shutting down factories, cutting back on burning coal and taking certain vehicle classes off the roads on days when pollution hits unacceptable levels, the official Xinhua news agency reported on Sunday.

Air quality in Beijing, on many days degrees of magnitude below minimum international health standards for breathability, is of increasing concern to China's leadership because it plays into popular resentment over political privilege and rising inequality in the world's second-largest economy.

Domestic media have run stories describing the expensive air purifiers government officials enjoy in their homes and offices, alongside reports of special organic farms so cadres need not risk suffering from recurring food safety scandals.

Smog blanketed most of the city from late Friday, prompting the government to warn people to reduce outdoor activities.

Transparent approach

On Saturday, an index measuring PM2.5, or particulate matter with a diameter of 2.5 micrometres (PM2.5), rose as high as 400 in some parts in the city.

A level above 300 is considered hazardous, while the World Health Organisation recommends a daily level of no more than 20.

The reading was still lower than last weekend, when it hit a staggering 755.

Lung cancer rates in the city have shot upward by 60 percent in the last decade, according to a report by the state-run China Daily in 2011, even as smoking rates have flattened out.

The pollution has also deterred foreigners from living and working in "Greyjing". Now it appears that the

government has adopted a more transparent approach to addressing the problem than in the past.

Officials once tried to spin the city's poor air quality by not including PM2.5 readings in reports and referring to smog as "fog" in weather reports. One official accused the US Embassy in Beijing of meddling in China's internal affairs for publishing its own PM2.5 readings online.

But this time around, state media appears to have been cleared to cover pollution as a major problem.

Vice Premier Li Keqiang, who is expected to take over as premier in March, said earlier this week that tackling pollution would be a long-term process.