China's rural-urban wealth gap was the widest last year since the nation launched its economic transformation three decades ago, state media said Tuesday, amid concerns the disparity could spark unrest.

Urban per capita income stood at 17,175 yuan (2,500 dollars) in 2009, compared to 5,153 yuan in the countryside, a ratio of 3.33 to 1, according to data released by the National Bureau of Statistics.

The agency did not compare that to previous years, but the China Daily newspaper said it was the widest gap since Beijing launched reforms in 1978 that set it on a capitalist path.

The disparity, arising from rapid economic development in coastal areas and cities, while the vast interior has lagged behind, has become a key concern of China's leaders as they seek to maintain social stability and prevent unrest.

The government has announced several new policies recently aimed at addressing the problem by spurring economic development in rural areas which are home to about 900 million people and stitching up holes in social safety nets.

There has also been a swelling chorus for reform of a household registration system that prevents China's roughly 230 million poor migrant workers from gaining residency in areas other than their hometown.

This denies them access to public services such as unemployment and health insurance, and free public schooling for their children, forcing many to use precious savings to pay for them.

On Monday, 13 major state-controlled newspapers around the country ran a rare joint editorial calling for abolition of the system, which it said "shackles the people's rights."

The system of registered permanent residence, known in China as the "hukou", is blamed for turning holders into virtual second-class citizens in areas where they have relocated in search of work and perpetuating the wealth divide.

It is rare for China's media to challenge a government policy. However, the government itself vowed recently to reform it.

The urban-rural divide is expected to figure prominently during the annual session of the rubber-stamp National People's Congress, which opens on Friday.

Premier Wen Jiabao singled out the wealth gap and hukou issue as pressing tasks for the government in a rare webcast at the weekend during which he fielded questions from online users.

"It is unfair if a society's wealth is only in the hands of a few people. In that case, the society is doomed to instability," Wen said.

The hukou system was used in the 1950s to curb destabilising population movements in a nation recovering from civil war, but was eased under China's economic reforms to allow cheap labour to migrate to manufacturing hubs.