The United Nations' top Human Rights official Michelle Bachelet is urging the Scott Morrison government to reform both the criminal and refugee detention systems.

Speaking at the Australian Human Rights Commission's Free and Equal conference in Sydney, the former Chilean president hit the Morrison government's treatment of asylum seekers both onshore and offshore.

"Mandatory detention is a mainstay of Australia's migration and asylum system," Ms. Bachelet said.  "The people it affects have largely committed no crime; many of them are in very vulnerable situations, and some are children, yet they are subjected to prolonged, indefinite and effectively unreviewable confinement.

"This includes those who remain in the offshore centres such as Nauru and Manus Island," she continued.  "We have a wealth of evidence to demonstrate the harmful effect this has on their mental and physical well-being."

Bachelet, a pediatrician by training, was "shocked" to learn that Australia's age of criminal responsibility was just 10 years old, a policy that disproportionately affects indigenous children, who make up 70 percent of those aged under 14 held in Australian jails.

She urged Australia to raise that age to the "internationally accepted level" of 14 years.  And Bachelet called on the government to enshrine comprehensive human rights protections in law and introduce constitutional recognition of Aboriginal and Torres Strait Islander people.  

This came a few days after Morrison's comments that were mostly seen as a swipe against the United Nations and international scrutiny of Australia's off-shoring of asylum seekers.  Taking a cue from the trend of right-wing nationalism, Morrison railed against what he called and "ill-defined borderless global community" and "unaccountable internationalist bureaucracy", and the government "can never answer to a higher authority than the people of Australia".