Asylum seekers being detained by Australia in Papua New Guinea should be made aware of their right to challenge their detention under PNG law, a human rights group says.
PNG's Supreme Court on Wednesday ruled Opposition Leader Belden Namah has the standing to challenge the constitutionality of Australia's Manus Island detention centre.
The court in its ruling also queried if detainees knew they could avail themselves protections under PNG's constitution.
Human Rights Watch Australian director Elaine Pearson says one barrier to bringing a successful court challenge is that lawyers do not have access to detainees.
"Only a few lawyers have been able to talk to detainees by phone," Ms Pearson told AAP on Thursday.
"That's one of the practical problems that needs to be dealt with. Lawyers need to have access to Manus Island."
When asked if she thought the Australian government would inform detainees of their rights under PNG law, Ms Pearson replied "that's what should take place."
"They should be making them aware," she said.
In its ruling the court suggested that rights groups such as Human Rights Watch and Amnesty International may be given standing to mount cases on behalf of detainees.
Ms Pearson said Human Rights Watch will continue to work with other advocacy groups, while Amnesty told AAP it was not ruling anything out.
"We call on both the Australian and PNG governments to ensure that all detainees have the right of access to a lawyer of their choice," an Amnesty spokesperson told AAP.
The five-man bench ruled in a unanimous decision that Mr Namah had standing to mount a case, and dismissed arguments that he could not because he was not directly affected by the controversial scheme.
The court said procedures exist in PNG's constitution to enforce basic rights by persons who claim their rights have been infringed.
"There are factual issues to be determined, which are better dealt with by evidence from the persons who claim that their rights are contravened," the summarised judgement said.
A PNG court last year ordered that Mr Namah's lawyers were allowed to go to the asylum-seeker processing centre to interview detainees.
Mr Namah's lawyer, Loani Henao, said at the time his requests for access to the Manus Island facility had been denied.
In August PNG's foreign minister pledged to introduce legislation to stop constitutional challenges against the asylum-seeker processing centre.