A study says Germany's birth rate has slumped to the lowest in the world, prompting fears labour market shortages will damage the economy.
Its authors warned of the effects of a shrinking working-age population.
They said women's participation in the workforce would be key to the country's economic future.
In Germany, an average of 8.2 children were born per 1,000 inhabitants over the past five years, according to the study by German auditing firm BDO with the Hamburg Institute of International Economics (HWWI).
It said Japan saw 8.4 children born per 1,000 inhabitants over the same time period.
In Europe, Portugal and Italy came in second and third with an average of 9.0 and 9.3 children, respectively. France and the UK both had an average of 12.7 births per 1,000 inhabitants.
Meanwhile, the highest birth rates were in Africa, with Niger at the top of the list with 50 births per 1,000 people.
Higher wage costsGermany's falling birth rate means the percentage of people of working age in the country - between 20 and 65 - would drop from 61% to 54% by 2030, Henning Voepel, director of the HWWI, said in a statement (in German).
Arno Probst, a BDO board member, said employers in Germany faced higher wage costs as a result.
"Without strong labour markets, Germany cannot maintain its economic edge in the long run," he added.
Experts disagree over the reasons for Germany's low birth rate, as well as the ways to tackle the situation.
Mr Probst said the country would need young immigrant workers to fill the significant skills gap. And more women were needed in the workforce to avoid economic problems.
Germany has one of the highest migration rates in the world, but has also seen growing support for anti-immigration party Alternative fur Deutschland (AfD).
The latest birth rate figures comes despite efforts by Mrs Merkel's government to invest in childcare support.