The dismissals and detentions appeared to be in line with a push by Hu Jintao, the Communist Party chief and state president, to instil official accountability since he assumed power in 2002.
Yu Xuejun, spokesman for the National Population and Family Planning Commission, said the authorities had launched an investigation after receiving complaints of forced abortions and sterilisations by family planning officials in the city of Linyi this year.
"According to the results of a preliminary investigation, some persons concerned in a few counties and townships of Linyi did commit practices that violated the law ... while conducting family planning work," Yu said on the commission's website.
"Currently, the responsible persons have been removed from their posts. Some of them are being investigated for liabilities and some have been detained," Yu said without giving a figure for officials sacked and detained.
Yu urged commission staff to learn a lesson from the case and "correct any infringements on citizens' rights".
China's population exploded after Mao Zedong exhorted the people to multiply in the 1950s to make the country strong.
China, the world's most populous
nation, has 1.3 billion people
But China - now the world's most populous nation with 1.3 billion people - put the brakes on growth more than two decades ago, imposing the tough one-child policy in urban areas.
A hefty fine is slapped on urban residents with more than one child. Rural people and members of ethnic minority groups are allowed a maximum of two children.
International human rights groups have accused overzealous Chinese family planners of forcing women to abort, in some cases in the ninth month of pregnancy, or to undergo hysterectomies, but Beijing regularly denies the claims or keeps silent.
Tuesday's rare admission of official wrongdoing came after a blind activist, Chen Guangcheng, accused Linyi officials of forcing couples with two children to be sterilised and forcing women pregnant with a third child to undergo abortions.
"It falls far short of the number of officials who should be punished," Chen, who has since been put under house arrest in Shandong, said on Tuesday.
A source close to Chen said about 120,000 Linyi residents had been forced to undergo abortions or sterilisation, but a Shandong family planning official said the figure was an exaggeration.
Allegations of police brutality
Linyi police took into custody and beat up family members and neighbours of couples who had fled to avoid the forced procedures, said the source, who spoke on condition of anonymity. Some died in detention.
"Only lower-level officials will be punished. The Linyi mayor and town chiefs won't be punished," the source said by telephone.
Chen was stopped from going to Beijing this month and held by police for about 30 hours. He staged intermittent hunger strikes and was joined by more than 10 local residents, two of whom are still in detention.