The generation of "only" children numbers 90 million.

The one-child policy has helped prevent 400 million births - about the size of the US and Mexican populations combined - and aided China's rapid economic development.

Despite that, Zhao said surveys have shown that 60 percent of Chinese would prefer to have two children, but that the government has no plan to relax birth limits.

Critics say the policy has led to forced abortions and a dangerously imbalanced sex ratio due to a traditional preference for male heirs, which has prompted countless families to abort female fetuses in hopes of getting boys.

Zhao blamed the imbalanced sex ratio on a traditional preference for boys and the availability of gender testing of fetuses with sonograms. She said the government was addressing the problem with education, subsidies and strict regulation of sonograms.

In 2005, the government began giving US$150 annual pensions to older couples with a daughter as a reward for complying with the policy and as an incentive to others to have just one girl baby.

Government statistics show that 117 boys are born for every 100 girls in China, well above the average for industrialized countries of between 104 and 107 boys for every 100 girls.

Experts have said the gender imbalance resulting from sex-selective abortions and other practices could have dangerous social consequences due to anticipated shortages of marriageable young women.