About a third of 18-year-old women in Japan may never have children, a government institute said on Wednesday, in the latest indication of an uphill battle to reverse a dwindling population in the world's third-largest economy.

The National Institute of Population and Social Security Research (IPSS) estimated in a report that 33.4% of women born in 2005 would be childless. The most optimistic scenario had that number at 24.6% and the worst at 42%.

Prime Minister Fumio Kishida in June promised to tackle the population crisis with "unprecedented" measures including bigger payouts for families with three or more children.