May 31 (Reuters) - China said on Monday that married couples may have up to three children, replacing the existing limit of two after recent data showed a dramatic decline in births in the world's most populous country.

Here are some of the milestones in China's efforts to steer population growth.

* China officially launched its controversial one-child policy in 1979, saying efforts to reduce poverty and develop the economy were being undermined by rapid population growth, especially in the countryside.

* Urban couples were allowed to have a second child if the parents were both single children, and there were looser restrictions on rural couples, meaning many had two children.

* In 2015, China began a campaign against illegal prenatal gender tests and sex-selective abortions to help address a gender imbalance, state news agency Xinhua said. China has a traditional bias for sons.

* The world's most populous nation in 2016 allowed couples to have a second child in a bid to address the rapid increase in the elderly as well as a dwindling workforce.

* Despite the relaxation, the number of live births per 1,000 people fell to a record low of 10.48 in 2019, down from 10.94 in 2018, according to government statistics.

* The number of new births in China plummeted 15% in 2020 from 2019, according to the Ministry of Public Security, with the onset of the coronavirus disrupting the economy and weighing on decisions to have a family.

* China's state planner said in March it would make the country's birth policy "more inclusive", while trying to reduce the costs of having children, amid mounting concerns over the country's rapidly ageing population.

* China could see its number of births slide below 10 million annually in the next five years if the government does not quickly abolish its policy of limiting families to two children, Dong Yuzheng, director at the Guangdong Academy of Population Development, told Yicai, a Chinese financial news outlet, in April.

* China's population grew at its slowest in the last decade since the 1950s as births declined, a census in May showed, fuelling pressure on Beijing to ramp up incentives for couples to have more children.

* In a major policy shift, China on Monday announced a new three-child policy.

(Compiled by Nick Macfie; Editing by Jacqueline Wong)