The quake happened at 5.08am, centred 25 kilometres west of Wellington at a depth of 31km.
Wellington Region Emergency Management said on its Facebook page there was no tsunami warning.
Wellington transport operator Metlink said it was replacing trains with buses until further notice.
The National Emergency Management Agency told RNZ it had no reports of damage yet, and was not yet considering activating a response.
A person in the suburb of Johnsonville told RNZ items fell off their shelves, while a Whanganui resident said it was felt quite strongly there.
So far more than 37,000 people have reported feeling it to the Geonet website, from as far north as Auckland's North Shore down to Invercargill in the south.
A listener in the Wellington suburb of Ōwhiro Bay said it was "a mean jolt, like a truck hitting the house, it rocked the house".
And a listener in Blenheim reported: "Heard quake coming, as we often do here - a heavy freight train getting closer, rumbling sound increasing before strong creaking jolt."
Further from the epicentre, in Whanganui, another listener experienced "fine trembling as lead in, then rocking with window sash weights noisy in old two-storey wooden home".
One person on Meta-owned social media site Threads described it as the "strongest quake I've felt since those ones in 2016". Another said it "felt stronger than a 5.8".
"Well that's a check for damage in the morning one," one person wrote on Bluesky. "The whole house bounced up and down," said another.
Several people reported the quake woke them - and the city's birdlife - up.
"Holy f***in sh****lls, that went on for ages," one person posted in the quake's immediate aftermath. "I DO NOT ENJOY THE SHAKEY WAKEY," said another.
"A lot of shaking at the World Famous Bucket Fountain!," an account on X (formerly Twitter) devoted to the iconic Cuba Street attraction said.
Fire and Emergency NZ told RNZ it responded to assist one person in Northland because a door frame had warped and they could not get out. That was so far the only report of damage.
'Timely reminder'
Wellington Region Emergency Management Office regional manager Jeremy Holmes called it a "significant shake for the capital".
"Based on the reports and the conversations we've had with various people around the region, it looks as though there were no significant impacts, which is great news."
He expected once people had a chance to survey their properties in daylight, there might be some damage reported.
"It's just a timely reminder that earthquakes can happen at any time, there is the possibility of aftershocks and that people should be looking to drop, cover and hold if there should be any aftershocks."
Just on Saturday, emergency response teams from across the North Island took part in an exercise in Wellington to test their ability to respond to a large earthquake.
