The Coalition of Aboriginal Peak Organisations NSW says the state government must act to end deaths in custody and over-incarceration of Indigenous people, including by immediately establishing a special sentencing court.

"Governments must shift from delivering systems predicated on disadvantage to facilitating the aspirations, priorities and self-determination of Aboriginal peoples," NSW CAPO co-chair and NSW Aboriginal Land Council deputy chair Charles Lynch said in a statement on Tuesday.

The NSW Coroners Court has in recent weeks heard details of the deaths of two Aboriginal men in custody.

Nathan Reynolds died of an asthma attack in September 2018 while an inmate in a Sydney prison. The 36-year-old had serious asthma, but the prison's medical staff did not develop a plan to manage his condition, his inquest heard.

An inquest into the death of Dwayne Johnstone, shot in the back by a corrective services officer as he tried to escape custody in Lismore in March 2019, was halted last week so the officer's conduct could be referred to the Director of Public Prosecutions for investigation.

A serving NSW police officer was also convicted on October 20 of assaulting an Indigenous 18-year-old man in custody.

NSW CAPO's demands include the establishment of a Walama Court - a dedicated, culturally-specific court for Aboriginal people involved in the criminal justice system.

The group is also calling for independent investigations of all deaths in custody and police misconduct, ambitious state-based justice targets, and for the age of legal responsibility to increase to 14.

Link-Up NSW chief executive Janelle Clarke said past government policies including separation of families and forced child removals had led to long-lasting impacts on Aboriginal people and communities.

"Greater investment into supporting our people through culturally appropriate reunification programs, counselling services and the use of circle sentencing such as Walama Court would serve our people better than the harsh and unjust treatment they receive from the justice system," Ms Clarke said.

A NSW upper house inquiry into the over-representation of Indigenous people in custody and reviews of Indigenous deaths in custody held hearings over two days last week.

NSW CAPO says the government should use the inquiry process as an opportunity to radically transform the justice system.

At least 21 Indigenous people have died in NSW custody since 2008.

Nationwide, more than 400 Aboriginal and Torres Strait Islander people have died in custody since the Royal Commission into Aboriginal Deaths in Custody was completed in 1991.

NSW custody statistics from June 2020 show more than a quarter of the state prison population is Indigenous.

Indigenous people in NSW were more than nine times more likely than non-Indigenous people to be imprisoned last year.

Australian Associated Press