The quake, which struck at 3.52pm (9.52 Thai time), was centred in the North Island about 115 kilometres northeast of the capital Wellington, according to the US Geological Survey.
The tremor hit at a depth of 27 kilometres and was widely felt throughout the North and South islands. It was followed by a series of smaller aftershocks.
New Zealand is on the boundary of the Australian and Pacific tectonic plates, forming part of the so-called "Ring of Fire", and experiences up to 15,000 tremors a year.
A devastating 6.3-magnitude temblor in the South Island city of Christchurch in 2011 killed 185 people -- one of the tiny nation's deadliest disasters of the modern era.
Wellington was the scene of the country's most powerful earthquake in 1855.
That devastating 8.2-magnitude quake caused four deaths and changed the city's entire geography, pushing the shoreline out 200 metres as it thrust the harbour floor upwards.