A fire engine outside the GCSB's headquarters in Wellington. - Photo: RNZ / Charlie Dreaver
The police have called in a specialist to test an unknown white powder which was sent to the building housing the spy agencies the GCSB and the SIS in Wellington.
Part of the building has been cordoned off as a precaution, after the letter was found around 3pm.
The police and Fire and Emergency are at the scene, and say they're working to ensure the safety of staff.
This afternoon Prime Minister Jacinda Ardern has announced that there will be a Royal Commission of Inquiry into security agencies following the Christchurch terrorist attacks that killed 50 people.