China's census shows its population grew to 1.34 billion people by 2010, with a sharp rise in those over 60.
Nearly half of all Chinese now live in cities and people over the age of 60 now account for 13.3% of the population, up nearly 3% since 2000.
But the figures reveal that China's population is growing more slowly than in the past.
That could affect the economy, as the number of potential workers, especially from rural areas, could shrink.
The proportion of mainland Chinese people aged 14 or younger was 16.6%, down by 6.29 percentage points from the last census in 2000.
The number aged 60 or older grew to 13.26%, up 2.93 percentage points.
When China carried out its first census in 1953 it had a population of 594 million, less than half the current figure.
This census, the first in 10 years, comes after a decade of rapid economic growth that has led to significant social change.
The results revealed that almost half of all Chinese - 49.7% of the population - now live in cities, up from about 36% 10 years ago. Many have been drawn to jobs in China's factories and coastal industrial zones.
The census for the first time counted migrant workers where they were living, rather than where they were registered. It found that more than 220 million Chinese had worked away from home for over six months in 2010, almost double the previous figure.
The government's strict controls on family size, including its one-child policy for most urban families, have reduced annual population growth to below 1% percent. The rate is projected to turn negative in coming decades.
There has been growing speculation in the country's media about the possibility that the government will ease the policy - introduced in 1980 as a temporary measure to curb surging population growth - and allow more people to have two children.
As it currently stands, most urban couples are limited to one child and rural families to two. The average household now numbers 3.1 people, down from 3.44 a decade ago.
Some demographers have said that the limits on family size may now threaten China's economic future, with fewer people left to pay and care for an older population, as well as to work in the factories that have transformed the country into the world's second largest economy.
"The data from this census show that our country faces some tensions and challenges regarding population, the economy and social development," said Ma Jiantang, head of the National Bureau of Statistics.
"First, the ageing trend is accelerating, and second the size of the mobile population is constantly expanding."
He said China would have to "actively respond to the new challenges in demographic development".
But state-run Xinhua news agency said President Hu Jintao told top party lawmakers on Tuesday that China's family planning policy would remain unchanged and the low birth-rate be maintained.