A 46-year-old Aboriginal man has died in Casuarina Prison, a maximum security prison in Western Australia.

The Department of Justice revealed on Tuesday morning that the man had been found unresponsive mid-afternoon on Monday in his cell at the prison's infirmary.

The Department said staff and then paramedics provided first aid to the man but he was declared deceased at the site. Preliminary reports indicated there were no suspicious circumstances, the Department said on Tuesday.

As is mandatory for all deaths in custody, WA Police will investigate and prepare a report for the State Coroner.

Justice advocates, who identified the man as Mr Hill, noted that the non-natural death rate in prisons is significantly higher for First Nations incarcerated people.

National Suicide Prevention and Trauma Recovery Project director Megan Krakouer told National Indigenous Times: "I am tired of our people dying by suicide or preventable causes."

"I call out the Department of Corrective Services who three years ago procured a Suicide Prevention Advisory Board, but we have not convened in more than two years. This tells you they do not care," she said.

Longtime advocate Gerry Georgatos told National Indigenous Times that "the younger the non-natural death, the higher the likelihood it is of it being a First Nations soul".

"Mr Hill died in the prison infirmary, of I suspect a suicide. That's beyond words of 'concerning'. It goes to the heart of depleted health care, of health discrimination. We have advocated for two decades for Medicare in prisons. If Medicare was in the prisons, Mr Hill may still be alive," he said.

"I understand Mr Hill had previously been briefly hospitalised for septiceamia. He believed his physical health had been deteriorating. Medicare funded bulk billing physicians in prisons are the most powerful advocates the incarcerated can have. No Medicare equals high non-natural deaths in custody."

A WA Department of Justice spokesperson told National Indigenous Times that following an independent review, the Department of Justice replaced the advisory board with a permanently staffed Suicide Prevention Governance Unit, which includes an Aboriginal Cultural Adviser.

"The unit has a broad mandate to improve oversight of practices to prevent suicide and self-harm in prisons and youth detention centres," they said.

It is understood that custodial facilities have specialised management units for at-risk prisoners to monitor their care, including hourly observations and 24-hour CCTV monitoring.

More than 500 Indigenous people have died in custody since the Royal Commission into Aboriginal Deaths in Custody brought down its findings in 1991.