Australia's most respected human rights lawyers have launched a constitutional challenge in Nauru to have 10 detained asylum seekers released from its detention centre, claiming it is unlawful, inhumane and degrading.

In documents obtained by Fairfax Media, four prominent lawyers - George Newhouse, Julian Burnside, David Hicks' lawyer Dan Mori and Jay Williams - allege the detainees have been held unlawfully and in ''indefinite detention'' since September 2012, without access to lawyers or a fair hearing, which they say is unconstitutional.

Mr Burnside said the detainees - men from Iran and Sri Lanka - had been held for an unreasonable amount of time, according to rules set by the United Nations High Commission for Refugees that stipulates it should take four to six months to process a refugee claim.

The lawyers argue that lengthy detention without asylum claims being processed is arbitrary and therefore unlawful under Nauru's constitution.

Mr Burnside said the delay was caused by Australia's ''no advantage'' law under which asylum seekers who arrive by boat must not be better off than refugees who come through official channels.

According to the court documents, lodged last week at the Nauruan Supreme Court, the men were flown to the detention centre and given a document that said it would take ''several months'' for the Australian and Nauruan governments to develop a process to assess refugee claims.

Mr Newhouse said he was contacted by an asylum seeker who was in a desperate situation, saying his claims were yet to be processed and he was being held in appalling conditions with no hope of release.

Only three weeks ago the Nauruan government was thrown into chaos after its only magistrate, Peter Law, an Australian citizen, was deported by the Nauruan president after he issued two injunctions restraining the government from deporting two residents without giving them any reason or right to challenge the action.

The president of the Australian Human Rights Commission, Gillian Triggs, was last week blocked from visiting the Nauru detention centre by Immigration Minister Scott Morrison on the grounds the commission's jurisdiction did not extend beyond Australia's borders.

A spokeswoman for Mr Morrison said the Nauruan government advises detainees that it will seek to make determinations in as ''short a time as possible''. She said timeframes would vary depending on many factors, including the availability of claims advice and the complexity of the application.

Do you know more? Email swhyte@fairfaxmedia.com.au

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