This earthquake was centred about 25km southwest of Taumarunui, a regional town approximately 200km south of Auckland.
There were a few unusual features. Firstly the depth — 207km — is quite rare for New Zealand, and most earthquakes of that depth occur around the Fiordland area of southwest South Island, not in the west of the North Island.
Beyond that, reports of where (and where not) it was felt vary very widely with some close-by locations not noticing it – a local government councillor just a few tens of kilometres away reported feeling nothing, yet there were strong reports from Christchurch around 500km away.
Generally, major earthquakes related to subduction zones are caused by "lumps and bumps" on the seafloor which struggle to slide past the lithosphere above – eventually they move with a big 'shock' hence the earthquake. Readers may observe that many of the very large earthquakes occurring along the Chilean coast can be matched with chains of undersea volcanic peaks – these have a major difficulty sliding under the South American plate.
The variability in perceived strength of the quake is due primarily to the depth, but this is tempered by various obstacles and free-flowing zones in the crust above which can guide and concentrate (or disseminate) the earthquake waves – much like the perceived signal strength of a far-off radio station where driving a short distance can yield stronger and weaker signal with no obvious reason.
No significant damage has been reported – this is entirely typical of deep volcanoes. In addition, there was no tsunami warning – the only time a tsunami can occur is when the earthquake is shallow, under water and includes vertical movement of the sea bed - none of those were true in this instance.