China is to outlaw the selective abortion of female foetuses to correct an imbalance in the ratio of boys to girls that has grown since the one-child policy was introduced more than 20 years ago.

Government figures show 119 boys are born in the world’s most populous country for every 100 girls, but Beijing has set the goal of reversing the imbalance by 2010, state media reported.

China implemented the one-child policy in the early 1980s to curb its massive population - which officially hit 1.3 billion on Thursday - but the restrictions have bolstered a traditional preference for baby boys.

“The government takes it as an urgent task to correct the gender imbalance of newborns,” the official Xinhua news agency quoted Zhang Weiqing, minister in charge of the National Population and Family Planning Commission, as saying in an overnight report.

“As a new measure, the commission will start drafting revisions to the Criminal Law in order to effectively ban foetus gender detection and selective abortion other than legitimate medical purposes,” Zhang said.

Sex-selective abortion is already banned but technologies such as ultrasound have made it easier to know a baby’s gender in advance, increasing the chances for aborting girls.

Xinhua quoted experts as saying criminalising the ban would be a more effective deterrent, but it gave no details on what possible punishments might be.

Chinese traditionally prefer sons because they are seen as more able to provide for the family, to support elderly parents and to carry on the family line. Daughters become members of their husband’s family when they marry.

Despite a desire to curb the sex imbalance and a relaxation in recent years that allows rural families to have two children if the first is a girl, China has shown no sign of abandoning the one-child policy and cracks down on those who advocate against it.

One such activist is Mao Hengfeng, who was dismissed in 1988 from her job at a Shanghai soap factory after becoming pregnant a second time.

Last April, the Shanghai public security bureau sentenced her to 18 months in a labour camp for campaigning against the one-child policy.

U.S.-based Human Rights in China said on Tuesday she had since had her sentence increased by three months.