The quake was centred in the Ashburton Lakes region of Canterbury, about 120km west of Christchurch, with a shallow depth of 10km.
Originally categorised as a 5.8 magnitude at 9.14am on Wednesday, it was upgraded to 6.4 and revised again to 6.2 by monitoring agency GeoNet shortly after.
"That was not light shaking," dairy farmer Craig Hickman said on social media platform X.
The earthquake was felt by thousands of New Zealanders, including those in Christchurch and Dunedin, 300km south.
Kiwis described the quake as rolling shaking lasting more than a minute.
Former Green MP Mojo Mathers was nearby, calling it "way too close for comfort!"
"Peel Forest pretty close to epicentre - whole house shook, cupboard doors swung open, flashbacks to the (Christchurch) quakes."
The devastating 2011 Christchurch earthquake, in which 185 people died, was a similar profile - a 6.2 magnitude at five kilometres underground - to Wednesday's tremor, but much closer to the South Island's biggest city.
That quake continues to haunt many Kiwis, with novelist Rachael King, in Christchurch, expressing a common sentiment of concern with her post.
"That was the kind of #eqnz that makes you worry there's a really big one happening somewhere far away," she said.
Kineta Booker said it was a "biggie" that caused signs to sway in Riccarton Mall in Christchurch.
GeoNet also registered eight aftershocks in the following 30 minutes, all which were indiscernible to humans.
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