Under forest plantings in residential red zone. Sorry about the photo, gunge on the lens. I have not seen this in Christchurch before but it is common nearby in Akaroa.
Taxon: Phytolacca americana (Synonym: Phytolacca decandra)
2012-08-22 Lower Austria, district Leibnitz, Sausal (490 msm Quadrant 9258/2)
German name: Amerika-Kermesbeere
ID source: Fischer & al., Exkursionsflora für Österreich, Liechtenstein und Südtirol (2008, 3rd edition); easy to distinguish from Ph. acinosa - Ph. americana grows substantially bigger and has hanging flower & fruit as shown here, while those of Ph. acinosa are standing upright
Habitat: broadleaf forest on most likely acidic soil
Occurrence: A newcomer to Austria (and Europe; native of Northern America) and in Austria naturalised only here in southern Styria (Südsteiermark). Here in Sausal the plant is obviously quite common and well established.
Also grown as cultivar, but rarely: a more common cultivar is its relative Ph. acinosa, which is also more commonly appearing as a naturalised newcomer.