Amnesty International says it is deeply concerned by the death in custody of a 25-year-old Aboriginal man in Darwin this week and is calling for a fully independent investigation into the circumstances surrounding his death.

The man died after being arrested by Northern Territory Police in Casuarina and placed in the rear cage of a police vehicle, where he was later found to be experiencing breathing difficulties before being taken to Royal Darwin Hospital where he died.

The international watchdog, which has campaigned for justice and human rights worldwide since 1961, said "no one should be at risk of dying simply because they have had an interaction with police".

"For First Nations people in Australia, this fear remains very real. Aboriginal and Torres Strait Islander people continue to be overrepresented in the criminal legal system and continue to die in custody decades after the Royal Commission into Aboriginal Deaths in Custody handed down its recommendations. Many of those recommendations remain unimplemented," they said in a statement issued Friday.

More than 600 Aboriginal and Torres Strait Islander people have died in custody in Australia since the Royal Commission issued more than 300 recommendations for reforms in 1991.

Amnesty International expressed "grave concerns" about the independence of the investigation into the young man's death, particularly given "police are involved in investigating deaths that occur during police custody or operations".

"Investigations into deaths in custody must be fully independent, transparent and culturally appropriate, and families must be kept informed throughout the process," Amnesty said.

"This death is not an isolated incident. It forms part of a broader pattern where First Nations people are disproportionately impacted by policing, incarceration and deaths in custody across Australia.

"Every death in custody represents a profound failure of duty of care."

The human rights group noted that governments and police have a legal and moral obligation to ensure that every person taken into custody is kept safe and returned home alive.

"Amnesty International stands with the family and community of the young man who died and calls for accountability, transparency and urgent action to prevent further deaths in custody."