The National Bureau of Statistics revealed that the proportion of China's population that is of working age fell last year for the first time since 2002, as the country struggles with a labour shortage.
The proportion of people aged between 15 and 64 dropped 0.10 percentage points to 74.4 percent, but the decline underscores the problems faced by the world's most populous country as its workforce shrinks.
"It is only a small shift, but there is a need to place much importance on the labour issue," said the NBS in a statement issued on Wednesday and reported by Chinese media on Thursday.
China's vast worker pool has powered the explosive growth of its export-driven economy over the past decade, but analysts say the labour supply is tightening up.
However, with fewer people available for certain jobs, workers have become louder in calling for better wages and the country has seen growing instances of unrest.
A series of strikes across China have taken place since November, as workers protest low salaries, wage cuts and poor conditions.
In the latest industrial action, about 2,000 steel workers in Sichuan's provincial capital of Chengdu walked off the job earlier this month to protest against low salaries, according to the US-based rights group China Labor Watch.
The shortage is the result of demographic changes due to China's one-child policy, introduced two decades ago.
The NBS said the proportion of people aged over 65 rose by 0.25 percentage points to 9.1 percent in 2011.