BEIJING » Thirty-five years after it slammed the brakes on population growth by adopting a one-child policy, China announced Thursday that it would allow all couples to have two children.

The momentous move, revealed in a brief communique from senior Communist Party leaders Thursday night, comes as China is confronting slowing growth and a rapidly aging society, with the number of working-age people shrinking for three years in a row.

Though China remains the world’s most populous nation, with 1.3 billion people, the population is expected to peak between 2020 and 2030 and then decline unless the birthrate — now 1.18 children per woman — starts rising.

Chinese officials have credited the one-child policy — adopted in 1980 at the dawn of China’s reform and opening era — with preventing 400 million births and helping the nation rapidly improve its economic fortunes and limit even greater strains on natural resources.

But in the West and in many parts of China, the policy’s implementation was criticized as overly harsh and even inhumane, with those who violated the rules subject to forced abortions and sterilizations and penalties including fines, harassment or the loss of their jobs.

Even recently, couples have complained that authorities have forced them to give up their second children. Some parents have come forward with harrowing stories of babies who were taken away by fraud or kidnapping — sometimes by government authorities who delivered them to orphanages and collected payments, claiming that the children (mostly girls) had been abandoned.

That has led to a decline in the number of Chinese children adopted by Americans and other foreigners, who didn’t want to be part of such coercive treatment.

But there have long been many exceptions to the policy, and in late 2013, Chinese officials announced a major reform that allowed couples in which one of the parents was an only child to have a second baby.

"The news that China is to end its notorious one-child policy hardly comes out of the blue," said Peter Lloyd Sherlock, a professor of social policy and international development at the University of East Anglia in England. "In reality, the policy has been phasing out over the past 15 years, with a reduction of sanctions in many parts of the country."

Still, the changes in late 2013 did not lead to a huge surge in births. The National Health and Family Planning Commission said China recorded 16.9 million births in 2014, up 470,000 from 2013, which showed the new policy was having some effect. But by May of this year, only 1.45 million couples — out of 11 million eligible ones — had applied to have a second child. Like many couples in the West, a fair number of Chinese couples, particularly in urban areas, appear to have decided that having a second child is too expensive or too much trouble.

Still, an unscientific survey of users on the Chinese social media platform Weibo conducted Thursday night showed 62 percent out of 30,000 respondents saying they would like to have a second child.

"A sigh of relief. In my lifetime, I don’t have to witness the disappearance of words like ‘brother,’ ‘sister,’ ‘aunt’ and ‘uncle’ from the Chinese language," said He Caitou, a well-known blogger, after Thursday’s policy change was announced.

Details on the implementation of the new policy were not immediately forthcoming. "To boost the population’s balanced development, China will allow couples to have two children while continuing to hold on to family planning policy as a fundamental national policy and improve the population growth strategy," the official Xinhua News Agency said.

The effects of the one-child policy have rippled throughout China’s society and economy, and contributed to an oversupply of single men.

Because many couples preferred to have a boy rather than a girl if limited to one child, it was common for them to sex-select for boys or give up their girl babies. China now has 117 men for every 100 women, and in 2020, China is expected to have 30 million more men than women. One researcher just last week sparked controversy by suggesting men be allowed to share wives.

With men feeling pressure to have a home to attract a bride, families have pooled their resources to help their unmarried sons buy property.

While it’s still common around China to see red-and-white banners urging citizens to abide by family-planning rules, numerous exceptions have existed for years.

For example, minorities, fishermen, some handicapped people, and rural families whose first child was a girl have long been allowed to have more than one child; local officials had substantial discretion to allow second births. Families who weren’t exempt from the policy had to pay fines if they had a second or third child — or face other punishments.

And that policy included celebrities; famed movie director Zhang Yimou, renowned for films like "Hero" and "The House of Flying Daggers," last year paid $1.2 million in penalties after it was revealed that he has had two sons and a daughter.

Because of the one-child policy and rapid urbanization and rising incomes, China’s birthrate has fallen below the 2.5 per woman average globally and the 1.7 average in developed countries. A rate of 2.1 children per woman is considered the "replacement" rate to keep the population steady.

China’s working-age population — defined by the government as people between 16 and 59 — has fallen for three years in a row, according to the National Bureau of Statistics. It fell by 3.45 million in 2012, another 2.44 million in 2013, and 3.71 million in 2014. According to the United Nations, China’s pool of workers could shrink by a total of 61 million by 2030.

Moreover, China’s cohort of workers is getting old. By 2050, 25 percent of China’s population will be over the age of 65, while the number of young people who can support the retiree set will have shrunk. China now has a 5-to-1 worker-to-retiree ratio; if the birthrate were to continue as is, the ratio would be only 1.6 to 1 by 2040, demographers predict.

Supporting retirees is one problem. Some economists also warn that a graying country also likely means lower economic growth, because retirees are not as voracious consumers as young people. Chinese leaders are already facing other downward pressures on economic growth as the country tries to move away from export-dependent factory jobs and heavy investment in infrastructure projects such as roads and airports.

While many people both inside and outside China support ending the one-child policy on humanitarian grounds, a substantial number of experts question whether encouraging more people to have children will help China’s economy.

In a report this month, Beijing-based Cinda Securities cautioned that relaxing the one-child policy was not the catch-all solution to China’s economic strains. It said China should focus instead on improving the productivity of its laborers and on improving efficiency by allowing markets to play a greater role in its economy. Reforms to the legal system could also foster economic growth, it added.

The firm’s researchers also said the government should explore ways to give older people opportunities to work. China’s current retirement age is 55 for women and 60 for men. The government has proposed raising those limits incrementally.

"Even if changes in government population policy could lead to increased birthrate and solve the ‘problem’ of the aging population, the country would face a new problem of a booming population," the firm warned. "China already has a large population. … And more population growth will be a fatal trap for economic development because the country does not have enough resources."

Others said the move to allow married couples to have two children still means that the state will play an invasive role in families’ intimate affairs.

"The move to change China’s one-child policy is not enough. Couples that have two children could still be subjected to coercive and intrusive forms of contraception, and even forced abortions — which amount to torture," said William Nee, China researcher at Amnesty International.

"The state has no business regulating how many children people have. If China is serious about respecting human rights, the government should immediately end such invasive and punitive controls over people’s decisions to plan families and have children."

(Tommy Yang in the Los Angeles Times’ Beijing bureau contributed to this report.)