The largest of a series of tremors that have shaken the region in the past few days, the quake knocked items off shelves, shattered some windows and brought trains in the capital, Wellington, to a halt.
"We've had one report of structural damage so far, but as far as I know, power in the city is still on," said a spokesman at the capital's fire station.
The quake's epicentre was in the Cook Strait that separates the country's North and South islands. Domestic media have reported some power outages in the South Island.
The Pacific tsunami warning centre has not issued a tsunami warning.