An earthquake of magnitude 6.9 has struck New Zealand, but there was no immediate report of major damage or injuries.

It was the largest of a series of tremors that have shaken the region in the past few days.

The earthquake knocked items off shelves, shattered some windows and brought trains in the capital, Wellington, to a halt.

The Pacific tsunami warning centre did not issue a tsunami warning.

"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 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.