A New Zealand high court judge has ruled that an alleged people smuggler living in Auckland cannot be extradited to Australia.

In his judgment, Justice Edwin Wylie upheld an appeal by Maythem Radhi to an earlier ruling that he was eligible for extradition to Australia.

Australian Federal Police allege that Radhi helped organise the ill-fated voyage of the SIEV X which sank en route to Christmas Island in 2001, killing 353 people.

Radhi's defence lawyer had argued that in 2001 his client's alleged crimes would not have attracted a jail term in New Zealand of more than a year and therefore were not extraditable offences.

Justice Wylie agreed and said Radhi was not available for surrender to Australian authorities.