Nearly half of Japanese adults are not having sex, with more than a fifth of married men and women said they were too tired from work to make love.

Even more worrying, more than 20 per cent of all Japanese men between 25 and 29 said they had little or no interest in sex what so ever.

The country's birthrate is in such decline that the Japanese population is expected to drop by a third within the next 50 years.

Scroll down for video

Not hot, just bothered: Nearly a quarter of all Japanese women, single or married, said sex was too 'bothersome' (stock image)

Researchers at the Japan Family Planning Association found that 49.3 per cent - 48.3 per cent of men and 50.1 per cent of women, had not had sex in the past four weeks, the Telegraph reports.

Sex in marriages are in decline, with more than a fifth of men saying they were too exhausted when coming home from work.

Nearly a quarter of all women, single or married, said sex was too 'bothersome', and 17.8 per cent said they were too tired from work to attempt lovemaking.

These new figures are dealing another blow to efforts to stem the declining birthrate in Japan.

In Tokyo's metropolitan area. which has a population of 35 million people, just 250,000 babies are born each year.

All work and no play: More than a fifth of married men and 17.8 per cent of women said they were too tired from work to make love (stock image)

Android loving: A 2013 documentary explored the rising number of young Japanese men preferring virtual relationships to actual real-life women

This is a shockingly low figure when compared to Greater London's rate of 135,000 children born to a population of just 8.3million.

In 2013, a BBC Documentary called No Sex Please, We're Japanese looked into the declining rate of sex in Japan.

The show explored the emergence of young Japanese straight men preferring virtual relationships to actual real-life women.

'Why would you get into something as messy, as troubling, as disorienting as a relationship when you could have a virtual girlfriend, a virtual experience, that maybe is even superior to the reality?,' one young man, Roland, says in the documentary.

'I do know a number of men in Japan who use the role play games, the dating SIMS, even advances in pornography, and would rather experience the opposite sex that way than go through the challenges of relationships.'