The results of a national census conducted late last year show the proportion of elderly people in the country of 1.34 billion jumped, while that of young people plunged sharply. The census results, announced Thursday, also show that half the population now lives in cities.

The census adds data to the world-changing shifts under way in China in the past decade, as economic reforms raise living standards and pull more people off farms into the cities while families get smaller and the population ages.

China’s rapid aging has fueled worries over how long the country will be able to sustain its high economic growth, as fewer young people are available to work in factories and build the roads that transformed it into the world’s second biggest economy after the United States.

The census results show that people aged 60 and above comprise 13.3 percent of the population, up nearly 3 percentage points from 2000. Young people aged 14 and below accounted for 16.6 percent, down 6.3 percentage points from a decade ago.

Ma Jiantang, commissioner of the National Bureau of Statistics, told reporters that while the population is aging nationwide, the trend is more pronounced in coastal and more developed areas where the population is large and land is relatively scarce.

The results also showed that 49.7 percent of the population now lives in cities, up from about 36 percent 10 years ago.

The total population figure of 1.34 billion was released earlier this year. It increased by 73.9 million — equal to the population of Turkey, or California, Texas and Ohio combined — over the 10 years, a slower rate than in previous decades. The reduced growth reflects the results of the country’s one-child policy, which limits most urban couples to one child and rural families to two.

Wang Feng, a population expert and director of the Brookings-Tsinghua Center for Public Policy in Beijing, said the census results confirmed that China’s population has turned a corner, with massive migration flows and a fertility rate of no more than 1.5 children per couple.

“That is alarmingly low for a large country like China,” Wang said.

He said the numbers showed that China has added about 40 million people aged 60 or older in the past decade.

“We’re looking at a province in China or a large country in the world and that’s how many elderly people have been added,” Wang said. “This is only the beginning of an accelerating process, given that fertility is so low right now, population aging will only get more serious.”

There has been growing speculation among Chinese media, experts and ordinary people about whether the government will soon relax the one-child policy — introduced in 1980 as a temporary measure to curb surging population growth — and allow more people to have two children.

But leaders have expressed a desire to maintain the status quo. President Hu Jintao told a meeting of top Communist Party leaders convened Tuesday to discuss population issues that China will keep its strict family planning policy to keep the birth rate low. Asked about possible changes to the policy, statistics bureau commissioner Ma reiterated Hu’s position.

China credits its family planning limits with preventing 400 million additional births and helping break a traditional preference for large families that had perpetuated poverty. But there are serious concerns about the policy’s side effects, such as selective abortions of girls and a rapidly aging population.

The official Xinhua News Agency said Hu briefly touched on concerns about population structure and the growing number of older people at the meeting Tuesday, saying that social security and services for the elderly should be improved. He also called on officials to formulate strategies to cope with more retirees.

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Associated Press writer Alexa Olesen contributed to this report.