The changes were announced in a party document on proposals to open up the banking sector, improve law enforcement efforts, abolish its "re-education through labor" system and reduce the number of crimes subject to capital punishment, China's state-run news agency Xinhua reported.
Party officials, led by President Xi Jinping, endorsed 60 reform proposals during the conference that ended Tuesday, although the endorsements were announced Friday.
China's family planning policy, first introduced in the 1970s, currently stipulates a couple can have two children only if both parents are only children. The new policy says only one of the parents has to be an only child, Xinhua said.
The birth policy will be adjusted as necessary to promote "long-term balanced development of the population in China," the party document said.
"We must certainly have the courage and conviction to renew ourselves," Xi said in a statement. "Overcome all the cross-cutting restrictions, surmount the constraints of sectional interests, and have an active, engaged spirit in studying and putting forward reform proposals."
If enacted, the family planning relaxation represents the first significant nationwide easing of family-size restrictions, Wang Guangzhou, a Chinese Academy of Social Sciences demographer in Beijing, told The New York Times.
"This is the first time that a central document has clearly proposed allowing two children when a husband or wife is an only child," Wang told the newspaper in a telephone interview. "Now it's just talking about launching this, but the specific policies have to be developed at the operational level."
The committee also endorsed a proposal to expand the country's banking sector by allowing qualified private capital to set up small- and medium-sized banks, subject to regulation, Xinhua said.
Concerning the abolition of its "re-education through labor" program, Xinhua said laws relating to correction and punishment will be improved, as would and community-based programs that help return convicts to society.
China also would work to ban extracting confessions through torture and abuse, the document outlining the reforms said. Also, courts will be told to tighten the practice of dismissing illegally obtained evidence, among other things.
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