The number of parents choosing to have a second child has surged since Beijing loosened strict caps on family size in January 2016 to try to rejuvenate the ageing labour force.
Some 52 per cent of the 11.6 million babies born between January and August have an older sibling, said the state news agency Xinhua, citing Wang Peian, deputy head of the National Health and Family Planning Commission.
That compares to about 45 per cent in 2016, when 18.5 million babies were born in hospital, the highest since 2000, according to the report.
Since the late 1970s the world's most populous country had restricted most couples to only a single child, with violators facing fines and even forced abortions.
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But concern about an ageing population and a shrinking workforce saw the country loosen the policy at the beginning of 2016.
While some parents had long been allowed more than one child, the change allowed every family a second.
The report said China had allocated some 2.9 billion yuan ($440 million) to build maternity and pediatric hospitals last year and plans to add 140,000 more obstetricians and midwives by 2020.