PART 7 - PERSONS IN TRANSIT TO ICC OR SERVING SENTENCES IMPOSED BY ICC
Enforcement of sentences in New Zealand
141.
Prisoner to be held in custody—
(2) On arrival in New Zealand or, if the person is already in New Zealand when the sentence is imposed, on the imposition of the sentence, the ICC prisoner must be detained in accordance with the Corrections Act 2004 as if the prisoner had been sentenced to imprisonment under New Zealand law.
Conditions of imprisonment / detention - international treaty standards
EDIT.