Japan has a problem, a lack of children, and it seems likely there will be even fewer in the future.

Japanese researchers have now warned of a doomsday scenario if it carries on this way with the last child to be born there in 3011 and the Japanese people potentially disappearing a few generations later.

Academics from the city of Sendai, which was hit hard by last year's tsunami, calculate there are now 16.6 million children under the age of 14 now in Japan.

And they say that number is shrinking at a disturbing rate of one every 100 seconds.

So if you do the mathematics, as they did, then the country will have no children within a millennium.

Another study recently showed Japan's population is expected to fall a third from its current 127.7 million over the next century.

Government projections show the birth rate will hit just 1.35 children per woman within 50 years, well below the replacement rate.

Now academics have created a population clock to highlight the fall and encourage public debate on the issue.

Click here to see the clock on Tohoku University's website.

"By indicating it in figures, I want people to think about the problem of the falling birthrate with a sense of urgency," Professor Hiroshi Yoshida, who led the research team, told the Japan Times newspaper.

The clock will be kept up-to-date by adding the latest population data each year.

The question everybody asks is why is there a lack of children?

The answer seems to lie in several reasons.

One reason is the cost. Japan is an extremely expensive country and getting a child through college can wipe out a family's finances.

But research shows it goes much deeper than that as the Japanese state does throw a lot of money at people with children.

Another argument is that there are more effeminate men now called "Herbivores" there who are either not interested in sex or women don't find masculine enough.

Then some suggest many young Japanese people prefer "virtual" friends with a robot or on the internet, while others suggest their fascination with comics rather than relationships is the cause for a lack of babies.

A study was released earlier this year in which it showed Japan's young people are shunning the idea of marriage and having children.

The National Institute of Population and Social Security Research study also showed one in four unmarried men and women in their 30s had never had sex, and most young women preferred being single.

It also showed over 60 percent of unmarried young men didn't have a girlfriend, and nearly 50 percent of women of the same age weren't dating.

If that wasn't bad enough, young Japanese people are also, it seems, increasingly not interested in sex.

A survey by the Japan Family Planning Association found that 36 percent of males between 16 and 19 had "no interest" in sex.

Japan's falling birth rate could seem to be an interesting fact but of little consequence to a country like the United States, yet it could have a huge impact on how Japan interacts with the outside world in the future, even affecting how it supports international obligations and alliances.

"Japan will be more likely to prioritize healthcare than international security," Brad Glosserman and Tomoko Tsunada wrote in Foreign Policy Magazine. "Older societies are typically more risk-averse, and Japanese -- 'reluctant realists' at the best of times -- will be increasingly unwilling to put their most precious resource, their young, in harm's way," they said.

Japan's population isn't falling faster because people there are living longer.

Japan has a life expectancy of about 86 years for women and 79 for men at present, and the ages are expected to rise in the coming decades.

More than 20 percent of Japan's people are aged 65 or over, one of the highest proportions of elderly in the world.

Japan's graying population is a real problem for the country's leaders as they need to ensure the dwindling numbers of workers can pay for all the care needed for the growing army of pensioners.

And the elderly have increasingly more economic clout with Japanese companies targeting them increasingly.

One interesting figure has come out of the diaper manufacturer Unicharm.

It announced last week for the first time ever sales of its adult diapers were larger than those for babies.

But Japan's elderly may have increased economic power now but they know without more children the country is doomed.

"The universal longevity society is what we humans have longed for and what countries across the globe have been aiming for. Yet, in order for Japan, which is in the process of becoming one, to be truly considered as a model of universal longevity society, the country needs to recover the birth rate," Japan's Council of Aging warned in a letter to the prime minister.

The easy answer would be large-scale immigration from other Asian countries, but the Japanese public has historically opposed such a measure.

Despite concerns about the lack of babies, the country is still a very crowded place.

The majority of the population is packed into the coastal belts because the rest of the country is mostly mountains.

If you travel from Osaka through Kobe to the historic city of Kyoto, its impossible to see where one city ends and the other starts as the concrete conurbation spreads for hundreds of miles.

One Japanese friend discussed with me the fall in the birth rate and suggested to me if there are far fewer people there in the future it will be a much better place to live.