Mu called for a relaxation of the family planning policy throughout China and for every couple to be allowed to have two children. The family planning policy has been credited in the past 30 years with easing short-term population pressures, but has placed greater stresses on pension systems, led to there being fewer women than men in China and depleted the pool of able-bodied laborers.

The current average fertility rate in China is between 1.4 and 1.8, but should be maintained at 2.1 to ensure the replacement of the population over time, Mu said.

Yang Zhizhu, a former law professor in Beijing who sued local family planning authorities in January 2011 for having a second child and refusing to pay a fine of 240,642 yuan ($36,962), saw little reason to praise the relaxation of the rules in Beijing.

Fines on couples who have a second child, even if they are paid by fewer people, remain legally unjust, Yang told China Daily on Wednesday.

Meanwhile, the call for relaxing the one-child restriction is gaining momentum in other Chinese cities. Citing Zhang Feng, director of the provincial family planning commission, Guangzhou Daily reported earlier this month that Guangdong province would seek the central government's approval to try out allowing all couples to have a second child.

Wang Yuqing, deputy director of the Committee for Population, Resources and Environment under the Chinese People's Political Consultative Conference, said China may adjust its family planning policy during the 12th Five-Year Plan period (2011-2015).

Wang said birth rates in big cities like Beijing and Shanghai have been on the decline for years, and the size of the working-age population began to decrease since 2009.

A gradual relaxation of the policy, allowing couples to have a second child, will not lead to a sudden population increase, Wang said.