Japan's population is expected to fall to less than 90 million by 2055, compared with today's roughly 127.8 million, the Ministry of Health, Labor and Welfare said Wednesday.

The forecast is based on an estimate by the National Institute of Population and Social Security Research, an affiliate of the ministry, which made the projection on the assumption that the average Japanese woman will give birth to 1.26 children during her lifetime -- the fertility rate in 2005.

In an earlier population forecast in January 2002, the institute estimated the fertility rate would recover to 1.39.

According to the latest estimate, in 50 years Japanese aged 65 or older will double to around 41 percent of the total population, while those 14 or younger will comprise only about 8 percent.

"It has become apparent that the tendency for the number of children to decline has yet to improve," Chief Cabinet Secretary Yasuhisa Shiozaki said at a press conference, underscoring the government's alarm over the issue.

The institute's projections show the population aging at an accelerating rate and a growing impact on the country's social welfare systems and economy.

The ministry said it will study how the declining number of children and the graying of society will affect the pension system and announce its findings at the end of January.

Prime Minister Shinzo Abe has told reporters the government will take every possible step to stem the birthrate decline, citing support for those who have children or take maternity leave, as well as measures to encourage marriage and child-bearing.

"I want to say it will not lead to the collapse of the nation's pension system even if the latest projection comes true," Abe said.

The institute said it made the projections taking into consideration recent social trends, including late marriages by women and the rise in people choosing to remain single, as well as the declining number of children per family. The effects of current measures to curb the falling birthrate have not been factored in.

According to the estimate, the fertility rate is expected to start declining again in 2007 after rising to 1.29 in 2006, with the 2012-2013 rate projected to fall to 1.21. In a longer-term projection, the total population is forecast to fall to 44.59 million by 2105.