China's population climbed to 1.37 billion last year, 6.8 million higher than in 2014 but childbirths dropped by 320,000 in the same period despite relaxation of the one-child policy since 2013 showing the reluctance of couples to have a second child.

Around 16.55 million children were born in China in 2015, about 320,000 fewer than the previous year despite relaxation of the family planning policy in 2013.

The total population of the Chinese mainland stood at 1.37 billion in 2015, 6.8 million higher than in 2014, the National Bureau of Statistics (NBS) said today.

Population experts previously predicted that about 1 million more newborns should be born in 2015 than were born in 2014 due to the easing of the one-child policy in 2013 to allow more couples to have a second child.

Experts also expected the total number of newborn children to hit 18 million in 2015, state-run Global Times reported.

"The decrease in the number of newborns was caused by the low childbearing intentions of women in ideal childbearing age and shrinking number of those at the ideal age," Huang Wenzheng, a former Harvard University assistant professor and expert on population, told outlet yicai.Com.

China has permitted couples to have two children from this year, scrapping its one-child policy of 35 years.

Huang said that the impact of allowing all couples in China to have a second child was overestimated.

He expected that the number of births in 2017 is unlikely to exceed 17 million.

Echoing Huang, Yao Mei-xiong, deputy head of the Centre for Population Census of the Fujian Province Bureau of Statistics, said that China's population is set to experience negative growth every year after 2025, yicai.Com reported.

Zhai Zhenwu, chairman of the standing council of the China Population Association under the National Health and Family Planning Commission, told the Global Times that the impact of the relaxed policy will not be felt fully until 2016.

As all couples are now allowed to have two children as of January 1, the number of newborn second children will likely exceed 1 million, he said.

China introduced its family planning policy in the 1970s, and the government began limiting most couples to having one child in 1980.

The country relaxed the policy for the first time in 2013 by allowing couples to have a second child if either parent was an only child.

According to the NBS, the male population reached 704 million while the female population was about 670 million, leaving a male-to-female ratio of 105.02 to 100.

The bureau's statement also said that the number of people over the age of 65 reached 143 million, accounting for 10.5 per cent of China's overall population in 2015.

Meanwhile, the size of the labour force - people aged 16 to 59 - in proportion to the overall population decreased for the fourth year in a row.

Though China is still in the demographic dividend period, the country must work harder to tackle the foreseeable problems caused by an aging society and a shrinking labour force, Zhai said.