China's working-age population continued to decline last year, the government said Monday, as Beijing grapples with a demographic time bomb that is one of its biggest challenges.

The country introduced its controversial one-child policy in the late 1970s to control population growth, but its people are now ageing -- and increasingly male -- government statistics show.

The world's biggest national population rose by 6.7 million in 2013 to 1.361 billion, excluding Hong Kong, Macau and Taiwan, the National Bureau of Statistics said.

Almost 118 boys were born for every 100 girls.

The working-age population -- defined as those from 15 to 59 -- fell by 2.44 million to 920 million, adding to concerns about how the country will provide for the elderly with 202 million people now aged 60 or over.

2012 witnessed the first absolute drop in the working-age segment in "a considerable period of time", officials said last year, adding that the fall was expected to continue through to 2030.

As late as 1982, the proportion of the population aged 60 or over in China was just five percent but it now stands at 14.9 percent.

China also released a key inequality statistic for 2013 on Monday. It had changed slightly from 2012, which was the first year since 2000 that Beijing had released the sensitive figure.

The Gini coefficient is a commonly used measure of income inequality, with a figure of 0 representing perfect equality and 1 total inequality. Some academics view 0.40 as a warning line.

The figure peaked at 0.491 in 2008 before falling to 0.473 in 2013, a slight decrease from 0.474 in 2012.

China's wealth gap and population imbalances are major concerns for the ruling Communist Party, which places huge importance on preserving social stability to avoid any challenge to its grasp on power.