South African steam locomotives in New Zealand

This video is about a trio of South African Railways locomotives that were shipped to New Zealand in 1996. Two of them are 25NC class 4-8-4s, while the third is a GMAM class 4-8-2+2-8-4 Garratt. I don't really know anything about the history of these specific locomotives, and why they were brought to New Zealand in the first place. What I do know is that the trio were stored at Mainline Steam's Parnell Depot until 2015, in which year the depot was closed and demolished. While most of the Parnell locomotives and rolling stock were transferred south to the Glenbrook Vintage Railway, the South African engines were stored in the sidings adjacent to the Port of Auckland. Apparently this was due to them being too heavy for New Zealand track. In 2020, the two 25NCs and GMAM Garratt were relocated to Mercer, as the port sidings were being repurposed (for what exactly, I don't remember). The three engines, along with a spare engine unit for the Garratt, are now stored next to the North Island Main Trunk in Mercer.