South Korea’s demographic crisis has deepened with the release of data showing its birthrate – already the world’s lowest – fell to a new record low in 2023, despite billions of dollars in government schemes designed to persuade families to have more children.

Reports that South Korea’s population had shrunk for the fourth straight year came soon after neighbouring Japan reported a record decline in its population last year, along with a record fall in the number of births and the lowest number of marriages since the end of the second world war.

The average number of children a South Korean woman has during her lifetime fell to 0.72, from 0.78 in 2022 – a decline of nearly 8% – according to preliminary data from Statistics Korea, a government-affiliated body. The rate is well below the average of 2.1 children the country needs to maintain its current population of 51 million.

Since 2018, South Korea has been the only member of the Organisation for Economic Co-Operation and Development (OECD) to have a rate below 1. In addition, South Korean women give birth for the first time at the average age of 33.6 – the highest among OECD members.

If the low fertility rate persists, the population of Asia’s fifth-biggest economy is projected to almost halve to 26.8 million by 2100, according to the Institute for Health Metrics and Evaluation at the University of Washington in Seattle.

Lim Young-il, head of the population census division at Statistics Korea, told reporters: “The number of newborns in 2023 was 230,000, which was 19,200 fewer than the year before, representing a 7.7% decrease.”

Since 2006 the government has invested more than 360tn won ($270bn) in programmes to encourage couples to have more children, including cash subsidies, babysitting services and support for infertility treatment.

The current administration, led by the conservative president Yoon Suk Yeol, has made reversing the falling birthrate a national priority, and in December promised to come up with “extraordinary measures” to tackle the situation.

But financial and other inducements are failing to convince couples who cite skyrocketing child-rearing costs and property prices, a lack of well-paid jobs and the country’s cut-throat education system as obstacles to having bigger families.

Experts have said that cultural factors are also responsible, including the difficulty working mothers have juggling their jobs with the expectation that they are mainly responsible for household chores and childcare.

South Korea’s major political parties are showcasing policies to stem population decline ahead of April’s national assembly election, including more public housing and easier loans, in the hope of dampening growing alarm that the country is facing “national extinction”.

Being married is seen as a prerequisite to having children in South Korea, but marriages are also falling, with the cost of living often given as the main reason.

South Korea is not alone in the region in struggling with a rapidly ageing population and a lack of children.

The number of babies born in Japan in 2023 fell for an eighth straight year to a new low, government data showed this week, a year after the prime minister, Fumio Kishida, warned that the stubbornly low birthrate would soon threaten the country’s ability “to continue to function as a society”. The problem, he added, “cannot wait and cannot be postponed”.

The health and welfare ministry said 758,631 babies had been born in Japan last year – a 5.1% decline from the previous year and the lowest number of births since statistics were first compiled in 1899.

The number of marriages fell by 5.9% to 489,281 couples, falling below a half million for the first time in 90 years – one of the key reasons for the declining birthrate.

Many younger Japanese say they are reluctant to marry or have families due to poor job prospects and living costs that are rising faster than salaries, along with a corporate culture that makes it difficult for both parents to work.

Japan’s population of more than 125 million is projected to fall by about 30% to 87 million by 2070, with four out of every 10 people at age 65 or older.

The chief cabinet secretary, Yoshimasa Hayashi, said the declining birthrate had reached a “critical state”.

He told reporters: “The period over the next six years or so until 2030s, when the younger population will start declining rapidly, will be the last chance we have to try to reverse the trend. There is no time to waste.”