Half of Japanese adults are not having sex, with almost 20% of men saying they either have no interest or an extreme dislike of it.

Survey findings from the Japan Family Planning Association showed that 48.3% of men and 50.1% of women said they had not had sex in the last month.

Further to this, the survey saw a rise in the number of men who are not interested in sex, known in Japan as "herbivores". This was particularly prevalent among men aged between 25 and 29, with cases of 'herbivorism' increasing 2.5 fold, the Japan Times reports.

The lack of sex among men and women had increased by 5% in comparison to the findings from 2013.

Among married people, 36.2% of men said they did not have sex, while 50.3% of women said the same. Most men said they were too tired after work, while 15% said they had become sexually inactive following the birth of a child.

Women said they felt sex was "bothersome", or like men, were too tired from work.

The findings come amid a plummeting population – Japan's birthrate is so low the population is expected to drop by a third within the next 50 years.

In March last year, the government took steps to encourage more sex by funding matchmaking and dating services. Officials also arranged "konkatsu" parties for single people.

Experts are concerned that the falling population will reduce the labour force and place greater financial burdens on young people to take care of a rapidly ageing population.

Masanao Ozaki, the governor of Kochi prefecture, said: "I'm deeply concerned as to whether young workers in the future will be able to take on such a huge burden."