China is to relax its policy of restricting most couples to having only a single child, state media say.
In future, families will be allowed two children if one parent is an only child, the Xinhua news agency said.
The proposal follows this week's meeting of a key decision-making body of the governing Communist Party.
Other reforms include the abolition of "re-education through labour" camps and moves to boost the role of the private sector in the economy.
The BBC's Celia Hatton, in Beijing, says most of the changes have already been tested in parts of the country.
Officials announce their plans well in advance to gain the consensus they need, she adds.
The latest announcements are contained in a 22,000-word document released three days after the Third Plenum meeting of the Communist leadership in Beijing.
Traditionally reforms are expected from the Third Plenum, because new leaders are seen as having had time to consolidate power. President Xi Jinping took office last year.
The one-child policy would be "adjusted and improved step by step to promote 'long-term balanced development of the population in China'", Xinhua said.
China introduced its one-child policy at the end of the 1970s to curb rapid population growth.
But correspondents say the policy has become increasingly unpopular and that leaders fear the country's ageing population will both reduce the labour pool and exacerbate elderly care issues.
By 2050, more than a quarter of the population will be over 65.
The one-child policy has on the whole been strictly enforced, though some exceptions already exist, including for ethnic minorities.
In some cities, both parents must be only children in order to be allowed to have a second child.
In the countryside, families are allowed to have two children if the first is a girl.
Couples who flout the rules can face heavy fines, or possibly lose their property or their jobs.
Rights groups say the law has meant some women being coerced into abortions, which Beijing denies.
The traditional preference for boys has also created a gender imbalance as some couples opt for sex-selective abortions.
By the end of the decade, demographers say China will have 24 million "leftover men" who, because of China's gender imbalance, will not be able to find a wife.
Most of the elderly in China are still cared for by relatives, and only children from single-child parents face what is known as the 4-2-1 phenomenon.
When the child reaches working age, he or she could have to care for two parents and four grandparents in retirement.
'Improve human rights'
On Tuesday, when the Third Plenum ended, China's leaders also promised that the free market would play a bigger role, and farmers would have greater property rights over their land.
State firms will be required to pay larger dividends to the government, while private firms will be given a greater role in the economy.
There will be greater liberalisation in both interest rates and the free convertibility of the yuan. More overseas investment will be allowed.
There will also be an increase in the number of smaller banks and financial institutions funded by private capital.
Xinhua said the decision to do away with the "re-education through labour" camps was "part of efforts to improve human rights and judicial practices".
China's leaders had previously said they wanted to reform the system.
The network of camps created half a century ago holds tens of thousands of inmates.
Police panels have the power to sentence offenders to years in camps without trial.
Other reforms announced on Friday include a reduction in the number of crimes subject to the death penalty.