The High Court has ruled as valid a Northern Territory law allowing so-called paperless arrests.

The law was introduced last year to free police from paperwork, allowing them to arrest and detain people for minor crimes for up to four hours.

This included those arrested for offences such as drinking in public, swearing or making too much noise.

The offences would have previously been dealt with by on-the-spot fines.

Concerns were raised by a coroner after one detainee held under the law died in custody.

In August, coroner Greg Cavanagh said the laws were "manifestly unfair", disproportionately targeted Aboriginal people and should be scrapped.

Looking into the death of Aboriginal man Kumanjayi Langdon, Mr Cavanagh recounted the evidence of Sergeant Paul Smith, who said officers were "inundated" by the paperless arrests and protective custodies and were "under the pump" on the night of the death.

Mr Langdon, from Yuendumu in central Australia, died aged 59 in May 2015, three hours after being taken into police custody under the NT Government's paperless arrest system for "drinking in a regulated place".

The North Australian Aboriginal Justice Agency (NAAJA) told the High Court the law was unconstitutional because it breached the separation of powers doctrine between the courts and the Government and undermined the integrity of the courts.

A majority of the court found the law was valid and did not allow police to detain people for longer than reasonably practicable.

It found the powers the law carried did not detract from the courts.

The court referred further questions to a single High Court judge to determine the costs.

High Court decision is 'vindication': A-G

NT Attorney-General John Elferink said he believed the High Court ruling vindicated his Government's arguments.

Mr Elferink said the court's finding that the law was not punitive supported the Government's defence.

"They were never designed to be punitive in nature and they are not punitive in nature," Mr Elferink said.

"They are a method of the police being able to bring people into custody as they would under their normal power of arrest and nothing has changed. No new power has been conferred on the police through this legislation."

Mr Elferink said that following the decision, he had no plans to repeal or review his "paperless arrest" law.

"A person who feels they are not guilty of that offence can still have the matter heard in court if they so choose to do, and moreover a person held under the paperless arrest scheme would be held no longer than they would be otherwise if bail was being considered," Mr Elferink said.

NAAJA had argued that the law was punitive because it allowed the police to detain people for four hours without charge, for minor offences, and that only courts should have that power.

The agency said they went against the recommendations of the Royal Commission into Aboriginal Deaths in Custody, which were that people should be detained for the shortest period possible.

Despite the unsuccessful challenge, a representative from the NAAJA legal team said they believed the case had been worthwhile because of the court's comments about the law; namely that the law did not allow police to detain people for longer than necessary.

But Ruth Barson from the Human Rights Law Centre said the court had put limitations on how the police could use the powers.

"So that is, when police arrest someone and they decide how to deal with them, whether it's to issue them with an infringement notice, they can no longer detain them and similarly they must take them before a court, as soon as practicable," Ms Barson said.