An Aboriginal man has died in custody at Western Australia's Casuarina Prison.

The 46-year-old man was found unresponsive in his cell overnight, officials said on Wednesday.

Prison Officers and medical staff provided first aid to the man before St John Ambulance paramedics arrived.

The prisoner was declared deceased at the scene.

The Justice Department said preliminary reports indicate there were no suspicious circumstances.

WA Police are investigating and, as is mandatory for all deaths in custody, a report will be prepared for the State Coroner.

Almost 600 Indigenous people have died in custody since the Royal Commission into Aboriginal Deaths in Custody brought down its findings and made over 300 recommendations for reform in 1991.

Kurin Minang human rights expert and law academic Dr Hannah McGlade told National Indigenous Times there is an urgent need for "independent reviews of all deaths in custody".

"I believe we should adopt the ACT approach where such deaths are regarded as critical incidents that can be reviewed by the independent prison inspector office," she said.

"Coroners are not experts in prisons and deaths in custody, nor the relevant standards including UN guidelines. Families also must wait years for a coronial inquest. It's just not good enough."

Dr McGlade, who is a member of the United Nations Permanent Forum on Indigenous Issues, said the prison response that "there are 'no suspicious circumstances' ...is not a matter for them to determine, as independent reviews are required".

"Many prisoners have died because we have yet to remove hanging points from prisons, even though more than 30 years this was recommended by the Royal Commission into Aboriginal Deaths in Custody," she said.

"We're a rich state that have the resources to ensure this at the very least and failure to do so shows neglect and lack of care and concern for Aboriginal lives."