Pete's first stint in youth detention left a deep and lasting impression on him. At 14, he said he was sexually abused and beaten by fellow inmates at a juvenile correctional centre.

Key points: 136 former and current prisoners with disabilities from 14 prisons were interviewed by Human Rights Watch

136 former and current prisoners with disabilities from 14 prisons were interviewed by Human Rights Watch Of those interviewed, 41 reported experiencing physical violence at the hands of fellow prisoners or staff; 32 described being sexually assaulted by fellow prisoners or staff

Of those interviewed, 41 reported experiencing physical violence at the hands of fellow prisoners or staff; 32 described being sexually assaulted by fellow prisoners or staff HRW also noted nearly all those interviewed had been placed in solitary confinement at some point

"It went from physical to mental to sexual, and that's where I think a lot of my dramas began because I had my self-esteem kicked out of me," he said.

Pete (not his real name) has an intellectual disability, along with depression and anxiety. He said this meant he was an easy target for bullying.

"They tend to push you around a little bit more and think that you're just not a normal person," he explained.

At the age of 20, Pete was sent to an adult prison, where the physical and verbal abuse continued.

He developed post-traumatic stress disorder, and still suffers from regular episodes of anxiety and flashbacks.

Former inmate Pete (not his real name) said his disability meant he was an easy target for bullying. ( ABC News: Dominique Schwartz )

"The times that I have been beaten up, there has been no assistance," he said.

A new report by Human Rights Watch (HRW) suggests Pete's story is not uncommon. It has uncovered widespread instances of abuse of prisoners with disabilities in Australia.

The report found that while people with disabilities account for about 18 per cent of the country's population, they make up almost 50 per cent of people entering prisons.

Of the 136 former and current prisoners with disabilities interviewed, nearly a third reported experiencing physical violence at the hands of either fellow prisoners or staff, while almost a quarter described being sexually assaulted by fellow prisoners or staff.

"In prison, people with disabilities are often viewed as easy targets, as weak and are targeted by other prisoners," said HRW disability rights researcher Kriti Sharma.

"They are routinely bullied for their belongings; their medication can be taken away. If they resist, they can be beaten up."

Senior psychologist at the Brisbane Women's Correctional Centre, Emily Reedy, conceded that prison staff often struggled to help prisoners with disabilities.

"I don't think that the custodial staff are equipped to deal with the complex mental health and other disability behaviours," she said.

Allegations of abuse by prisoner-carers

Human Rights Watch noted cases where prison officers appointed other inmates as carers of people with disabilities.

The positions were particularly coveted because they were paid roles and helped to ease the burden on prison staff.

However the report documented several cases where prisoner-carers had previously been convicted of sex crimes or had been accused of sexual violence in prison.

One senior nurse in Queensland told HRW that six of the eight current prisoner-carers in their facility were convicted sex offenders.

"We had a case here where a prisoner with a disability was recently raped in custody by his carer," she said.

"During a random cell search, officers found blood and faeces on his bedsheets. Only then he disclosed he was raped on numerous occasions — before that he was too scared."

Ms Sharma said the prisoner-carer model put people with disabilities at risk.

"It means that the person is in the power of another inmate for 24 hours a day," she said.

In a statement, Queensland Corrective Services Commissioner Peter Martin said claims of alleged criminal offences relating to abuse of prisoners needed "to be properly assessed and investigated".

He said Queensland Corrective Services was in the process of developing a plan "which will further focus on issues relevant to the HRW report".

Western Australia's Department of Justice also responded, saying in a statement it had not been provided with any detail to corroborate the serious allegations raised by Human Rights Watch.

The department said when it was provided with information, it would look into the allegations and take appropriate action where necessary.

Solitary confinement 'exacerbating' mental illness

Prisons use solitary confinement for different reasons, including punishment to address behavioural issues. ( Supplied: Human Rights Watch )

The report also noted that nearly all the prisoners with disabilities who were interviewed had been placed in solitary confinement at some point.

These solitary confinement units, also known as "observation units", were often at capacity, and meant prisoners were locked in a small cell for up to 22 hours a day with no outside contact.

Prisons use solitary confinement for several different reasons, including punishment to address behavioural issues, but also to observe or "treat" patients who expressed feelings of depression or anxiety.

Ms Sharma said solitary confinement only exacerbated existing mental illness.

"While solitary confinement can be psychological harmful for any prisoner, it's devastating for prisoners with disabilities," she said.

Kriti Sharma said inmates with disabilities were often viewed as easy targets. ( ABC News: Rebecca Armitage )

"It pushes them to self-harm even more, often resulting in increased risk of suicide and while they're in solitary confinement they don't receive any meaningful mental health support, which is extremely disturbing."

Pete said he was held in solitary confinement for up to two weeks at a time while he was in prison.

"They treat you like a basket case. You're put in a smock with no undies, you are basically locked down for 22 hours a day," he said.

"I felt personally that it did more harm to my mental health than what it did good because I don't understand how someone can be put into that environment for so long and not have anything to stimulate your mind or talk to someone."

The report also found that Indigenous inmates with disabilities were subjected to targeted verbal and physical abuse, including racial slurs, with evidence of staff and prisoners engaging in racist language and behaviour in 11 out of the 14 prisons visited.

However Human Rights Watch said most prisoners were reluctant to report the abuse they had experienced, out of fear of being labelled as a traitor or facing further mistreatment.

Pete said he had struggled to come forward to share his story.

"I never told them, and when I did talk to a psychologist, I was still fearful of what I was telling them," he said.

"All the times that I have let my feelings out, they've locked me away in an environment away from the other inmates. All we are is a number to them, they've got no recognition of how to treat people properly."