Pan Guiyu, deputy director of the State Population and Family Planning Commission, said on Thursday that the policy had avoided 300 million births over 30 years, the equivalent, she said, to the population of Europe.
"The good effects are very apparent," she said. "But can we relax now? I should tell you we are still facing a grave situation."
China launched the one-child policy in the early 1980s to curb its population, now over 1.3 billion, but the restrictions have bolstered a traditional preference for baby boys and have come under fire from Western countries and human rights
Zhao Baige, vice-minister in charge of the commission, said earlier this month that the one-child policy had been misunderstood in the West, that in rural areas it allows for two children and in minority communities, there are no restrictions at all.
But she noted that the policy has caused a disparity
between the male and female population.
Sex-selective abortion is banned, but ultrasound has made it easier to know a baby's gender in advance, increasing the chances for aborting girls.
Chinese traditionally prefer sons because they are seen as more able to provide for the family, and government figures show 119 boys are born in China for every 100 girls.