BEIJING - China's one-child policy has created a generation of "only" children that now numbers 90 million, a senior family planning official said Friday.

From the beginning of the one-child policy at the end of the 1970s through last year, some 90 million children who would never have siblings have been born, most in cities, said Zhao Baige, vice minister for China's National Population and Family Planning Commission.

The Chinese government contends 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.

"We would have to study the effects, positive and negative, that might occur if we implemented a two-child policy," she said.

Critics say the policy has led to forced abortions, sterilizations 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 said there have been isolated cases of local officials forcing or ordering people to comply with family planning restrictions but insisted they were on the decline. She did not give specific figures or details.

She 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.

The government also allows rural families to have two children and ethnic minorities to have three. In recent years, it has let couples where both the husband and wife are only children to have two offspring to spread the burden of taking care of grandparents and parents when they retire.