China will loosen some restrictions on the free movement of workers within the country, long stymied by registration papers that limit access to critical social services, state media reported Saturday, although the new rules may leave many out in the cold.

The labour of hundreds of millions of migrants has helped achieve China's transformation from an overwhelmingly agrarian society under orthodox Communism to the world's second-largest economy.

But the country's "hukou" system of residency permits, established decades ago, continues to deny those who move, and their children, equal access to services like education and healthcare.

The rules have created a generation of 61 million "left behind children" often raised by their grandparents or other family members, with more than three percent simply left on their own, according to state media.

Another estimated 13 million Chinese citizens live without any documents at all, cursing them to a shadowy existence, with no access to basic public services or legal route to employment.

Premier Li Keqiang "recently" signed the cabinet order that promises to "improve basic public services in urban areas", according to a report by the Xinhua state news service, which added the rules would take effect on January 1 of next year.

Those who have obtained steady, legal work for more than six months will, in some cases, be eligible for better access to services, according to a copy of the rules posted on the cabinet's web site.

While that may make things easier for workers moving between the country's smaller cities, the provisions suggest they may be of little help to those seeking employment in so-called "mega cities" like Beijing or Shanghai, not to mention illegal living in the country's shadows.

Obtaining services requires getting a residence certificate, the new rules say, but acquiring the document requires legal proof of residence and employment, a Catch-22 that likely means the rules do not apply to many migrant workers.

The rules become increasingly strict in proportion to a city's size.

Getting a residence permit in Beijing, for example, requires proof of legal residence and employment, as well as proof of social insurance, continuous residence and a "perfect" score on a government point system.

The country tightly controls the number of people allowed to live in the capital and has made moves to check the growth of its population.

Although Beijing has repeatedly promised it will change the "hukou" system as part of structural reforms aimed at improving economic performance, changes have been incremental.