It's the social and health crisis plaguing almost one million Japanese people.

The sufferers of 'Hikikomori' – mostly young men - have such severe social withdrawal they isolate themselves in their bedroom, in some cases for years.

One of the few hikikomori experts in Japan, Dr Takahiro Kato, suffered from the condition as a student and is now working to prevent it from having a widespread affect on the next generation.

Dr Kato, who is studying hikikomori with a team of experts at Kyushu University in Fukuoka, said he had seen cases so severe that some men in their 50s had been withdrawn from society for more than 30 years.

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Sufferers of 'Hikikomori' have such severe social withdrawal they isolate themselves in their bedroom

Pictured is the subject of French documentary Hikikomori, A Deafening Silence - available online

The social and health crisis plaguing almost one million Japanese people, and affecting the country's economy

He said the sufferers, who refuse contact with friends and even family, are often 'intelligent and capable' young people meaning the problem is also a drain on the Japanese economy.

'I worry about it strongly because now about one per cent of the population withdraw like hikikomori or some similar state,' Dr Kato told Daily Mail Australia.

'Majority are after graduate university so economic impact is very terrible I think.

'Some hikimori have graduated from very good famous universities so it’s a very sad story for them.'

Yuto Onishi, 18, from Tokyo had not left his bedroom for almost three years before he sought treatment six months ago, ABC's 7.30 reported.

He spent his days asleep and nights surfing the internet and reading Japanese manga, and did not talk to anybody.

Mr Onishi said he believed his condition was triggered by an incident at junior high school when he failed as a class leader.

Sufferers, who withdraw from society and refuse contact with friends, are often 'intelligent and capable'

Yuto Onishi, 18, from Tokyo had not left his bedroom for almost three years before he sought treatment

He spent his days asleep and nights surfing the internet and reading manga, and did not talk to anybody

'Once you experience it, you lose reality,' Mr Onishi told 7.30.

'I knew it was abnormal but I didn't want to change. It felt safe here.'

The term hikikomori can refer to both the condition and the people who suffer from it.

Japan's Ministry of Health, Labor and Welfare defines hikikomori as people who do not participate in society - mainly work or study - and do not have any close non-familial relationships. Their symptoms must last for six months or longer, Tofugu reported.

Dr Kato said he believed many environmental contributed to hikikomori, with most cases arising in middle class families.

'It’s very rare to find hikikomori in poor families,' he said.

'So middle class environment, middle class families, have a high risk of hikikomori.

One of the few hikikomori experts in Japan, Dr Takahiro Kato, suffered from the condition as a student and is now working to prevent it from having a widespread affect on the next generation

'Majority of hikikomori are graduated people, after graduating university they became hikikomori.'

Many hikikomori stay locked in the bedroom of the family home, and often parents will support their children.

'Japan is very different from western society, for example the mother-child relationship is strongly different to western society,' Dr Kato said.

'Japanese parents are overprotective to their children. For some people it can be difficult to be independent.

'It’s one reason why Japan have many more hikikomori compared to western society.'

He added that: 'In Japanese society boys have very much more pressure to enter good university, good company and many - especially male - are under very, very strong pressure.'

Dr Kato said therapy is necessary for family members as well as sufferers in order to change the relationships and group dynamic.

Hikikomori and counsellors at Dr. Saito Tamaki's clinic at the Sofukai Sasaki Hospital near Tokyo

He is working with a team of experts at Kyushu University to study the social and biological factors that contribute to hikikomori in order to come up with a 'multi-dimensional diagnosis'.

'Most case studies have only focused on the psychological aspect, but hikikomori is not just about mental illness,' he told 7.30.

Treatment for sufferers involves rebuilding communication skills as a first step, with some having not talked to loved ones for years.

'The main therapy approach is psychotherapy - especially group psychotherapy because many hikikomori people do not communicate with others so they need to have some communication experience in a group,' Dr Kato said.

But with many hikikomori reluctant to talk to their own families, let alone seek treatment, Japan faces serious challenges in identifying the problem for future generations.