The quake hit at 5:09 pm (0509 GMT) 57 kilometres (36 miles) south-southwest of Wellington at a depth of 14 kilometres, the US Geological Survey said.
USGS initially reported the magnitude at 6.9.[break]
It was followed minutes later by another quake of 5.5 and came about 10 hours after a 5.8 tremor in the same region which has been rocked by multiple quakes in recent days.
Dozens of earthquakes were recorded on Sunday with New Zealand´s GeoNet earthquake monitoring service describing the 6.5 tremor which was felt widely as "severe".
"There was a rocking and rattling which lasted about 30 seconds," a resident in the South Island resort town of Nelson told AFP.
The fire service received multiple calls to assist people trapped in elevators in Wellington and the tremblor also set off sprinklers in city buildings and cut electricity supplies in many areas.
Seismologist Anna Kaiser told the New Zealand Herald that earthquakes of this magnitude were not unusual in the region.
"When we get one of these events there will be increased seismicity in the region and there´s always the possibility of a larger event but it´s unlikely."
The Pacific Tsunami Warning Centre said earthquakes of such magnitude can generate local tsunamis but there was no threat of a "destructive widespread tsunami ".
New Zealand´s civil defence authorities said it was "unlikely to have caused a tsunami that will pose a threat to New Zealand."
Recent quakes have been centred about 200 kilometres north of New Zealand´s second largest city Christchurch, where a 6.3-magnitude quake in February 2011 toppled buildings onto lunchtime crowds, leaving 185 people dead.
The country sits on the so-called "Ring of Fire", the boundary of the Australian and Pacific tectonic plates, and experiences up to 15,000 tremors a year.
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