China would by now have 400 million more people if a family planning policy ordering most couples to have just one child had not been put in place, said a top population official in Beijing on Wednesday.

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The family planning policy has stopped the population growing too fast, and contributed to China's socioeconomic development, said Zhang Weiqing, minister in charge of the State Population and Family Planning Commission, at the International Workshop for Senior Officials on Capacity-Building in Programme Management on Population and Development.

Formulated in the early 1970s, China's family planning policy encourages late marriage and late childbearing, and limits most urban couples to one child and most rural couples to two.

Zhang Weiqing pledged earlier this year that China will work to keep its mainland population below 1.37 billion by 2010. China officially announced its population had reached 1.3 billion with the birth of a boy in Jan. 2005.

Zhang has several times reiterated China's determination to pursue the family population policy, warning that there will be a baby boom in the next four years as the first only-child generation reaches childbearing age.

He also spoke of population problems yet to be addressed in China, in particular the aging population and sex ratio imbalances.

Earlier reports said China's elderly population has topped 143 million, while statistics show that 117 boys are born for every 100 girls in China, well above the international average of 104-107 boys.

Zhang stressed the importance of international cooperation and exchanges of population management experience during the on-going workshop, and offered to provide population management training and contraceptive supplies to developing countries.