A mainland population official admitted yesterday that China's birth-control policy had aggravated the country's gender imbalance, but stressed that the much-criticised guidelines would stand. National Population and Family Planning Commission director Zhang Weiqing said the gender imbalance was expected to worsen and the government would spend the next 10 to 15 years to put the ratio between boys and girls on a more even footing. In 2000, 117 boys were born for every 100 girls. 'Of course the gender imbalance has something to do with China's strict family planning policy,' he said. '[The policy] has aggravated the imbalance, but this doesn't mean the imbalance is a consequence of the policy.' Mr Zhang's remarks came after a survey pointed to growing discontent about rich people buying their way around the one-child policy to have a second child. The gender disparity has emerged as an alarming issue since the mainland introduced the one-child policy in 1979. The central government recently admitted the policy was a source of social disharmony. A recent government report estimated the mainland would have 40 million more men of marriageable age than women by 2020. Describing the situation as grave, Mr Zhang said the skewed sex ratio was also a result of the ingrained tradition of favouring boys over girls and the abuse of ultrasound scanning technology. Ultrasounds have been commonly used on the mainland for gender-specific abortions for parents wanting a boy as their only child. However, Mr Zhang said China's family planning was not a 'one-child' policy because that requirement only applied to 35.9 per cent of the mainland's population. He said 52.9 per cent of the population was allowed to give birth to a second child if their first was a girl and another 9.6 per cent were poor farmers who were permitted to have two children. About 1.6 per cent of the population were ethnic minorities who were allowed to have at least two children, he said. Mr Zhang said Beijing would 'unswervingly' continue its birth-control measures through to 2010 when the population was expected to reach 1.36 billion. He said restrictions would remain in place because of a baby boom in the 1980s. He said the 100 million or so only children born since the 1970s had reached marriageable age and relaxing the rule would result in another wave of births. 'It will be very risky if we allow a second child now,' he said.