ACT Corrections described it as "a necessary measure to assist in limiting the risk of infection to detainees, visitors and staff".

Additional precautionary measures also include detainees being asked additional screening questions by Justice Health Services.

The prospect of the pandemic reaching the prison population would be a chilling one for the ACT government given the close-packed human environment behind the jail's maximum security fencing.

While the population varies, around 470 male and female prisoners share the Alexander Maconochie Centre and without using the jail's special units, there are 424 beds according to details published in the Healthy Prisons Review last year.

"In practice, the AMC routinely accommodates a detainee population in excess of the design capacity by 'double-bunking' cells/rooms," the review said.

A typical cell is about nine square metres in size.

Over-population means prisoners are in constant close confines, with remandees waiting to be go to trial or to be sentenced mixed in with sentenced prisoners, a practice which creates a "revolving door" and increases the risk of the broader population's exposure to the virus.

Adding further complexity is the low levels of immunity and health of the Canberra prison population.

After South Australia banned smoking in its jails late last year, Canberra's prison is one of very few in Australia which permits smoking.

Almost a quarter of the jail population is on methadone treatment for a drug addiction.

Julie Tongs, the head of the ACT's Winnunga Aboriginal Health Service which has been operating a treatment service for indigenous detainees at AMC since October 2018, said that she held grave concerns for the prisoners and their physical and mental wellbeing.

"It's hard enough for us on the outside with all the new social distancing requirements and self-isolation which is occurring," she said.

"But consider how much more this will be affecting the detainees who only get snippets of the news and can't see their friends and family.

"I completely understand why the restriction [on visitors] is being put in place but it makes it terribly hard for the prisoners and their families.

"This is a highly vulnerable population and we can only hope that they [Corrections] are properly communicating to the detainees why this has to happen."

A survey of Canberra detainees last year found that 72 per cent found it was difficult to get psychological help when needed.

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Psychological services are provided by Corrections Psychological and Support Services but as at July 1 last year, there was just one psychologist for nearly 500 inmates.

The COVID-19 pandemic is already causing significant issues for prison populations elsewhere in the world. In parts of the US, inmates arrested for minor crimes and those most vulnerable to infection due to underlying health problems are being identified for early release.

A guard and a prisoner tested positive for coronavirus at the notorious Rikers Island prison in New York, where disgraced former Hollywood producer Harvey Weinstein is an inmate.

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