The first magnitude 5.9 quake occurred at 10.16am on Wednesday, and centred on Porangahau, a remote town in the sourthern Hawke's Bay region.
It was followed three minutes later by a 5.4 magnitude quake, one of more than a dozen aftershocks in the hour afterwards.
The earthquakes were shallow - the first measured at 21 kilometres underground - making them widely felt.
"Gosh, we're just having a massive earthquake here in Hawke's Bay," cricket legend Ian Smith said while broadcasting his SENZ Mornings show live from nearby Havelock North.
"Everything's still shaking. My goodness, that's a massive earthquake.
"Holy heck. I've never commentated on an earthquake before ... that is a long, prolonged, woah it's still going, bigger, bigger, bigger."
More than 22,000 people logged the first quake with GNS Science, most in the central North Island and Hawke's Bay.
"Under the desks in our Council meeting!" Palmerston North councillor Lorna Johnson tweeted.
"Two large shakes felt in Palmy."
The earthquakes were also felt by many in the capital Wellington, particularly those working in higher offices of multi-floor buildings.
Porangahau and surrounding regions were among those hit by Cyclone Gabrielle, with roads and lands damaged by landslips.
GNS Science warned the earthquakes may have caused further slips.
Initial concerns for a tsunami were erased by the National Emergency Management Agency 40 minutes later.
Another major earthquake struck Raoul Island, a New Zealand island about 1000 kilometres north-east of Auckland, two days ago.
There have been no reports of damage from the 7.3 magnitude quake.
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