The number of Indigenous people who have died in custody in Australia has hit the highest level since records began in 1980.

New data from the Australian Institute of Criminology showed 33 of the 113 people who died in custody in the 12 months to June this year were Indigenous, up from 24 compared to the previous corresponding period.

Aboriginal and Torres Strait Islander people are disproportionately represented in the criminal justice system, making up more than one-third of all prisoners, despite being less than four per cent of the country's population.

The figures come more than three decades after a landmark inquiry into Indigenous deaths in custody which made hundreds of recommendations.

Of the 33 Indigenous deaths in custody between last July and this June, 26 died while in prison custody, an increase from 18 in the previous 12-month period.