Seven Aboriginal people have died in custody across Australia in the last two months, following another two deaths confirmed in NSW and Victoria.
A man died at Port Phillip Prison in Melbourne's west on Monday night, Corrections Victoria said.
It is believed he suffered a medical episode. A smoking ceremony was being arranged.
Separately, NSW authorities confirmed a 37-year-old man was found dead in his cell at Cessnock Correctional Centre on Tuesday morning.
Both deaths have been reported to the coroner.
They follow the deaths of five other Aboriginal people in custody across Victoria, NSW and Western Australia since March 2.
They include a man aged in his 30s at a NSW prison hospital, and another man and a woman, at Victoria's Ravenhall Correctional Centre and in custody in NSW respectively.
Barkindji man Anzac Sullivan, 37, died during a police pursuit in Broken Hill and a 45-year-old man died in hospital in Perth.
NSW Greens MLC David Shoebridge said the deaths were a national crisis and reinforced the urgent need for the 339 recommendations of the Royal Commission into Deaths in Custody to be implemented.
"Every First Nations death in custody is an inevitable result of the racist criminal justice system that results in First Nations people in NSW being the most incarcerated people in the world," he said in a statement.
"The government is on notice and action is urgently required. It cannot be accepted that First Nations people routinely die in custody."
More than 470 Indigenous people have died in detention since a 1991 royal commission report into Aboriginal deaths in custody.
Australian Associated Press