"There was initially some concern there may have been a tsunami, but that possibility has now been discounted," Smith said.

The quake was near to the Auckland Islands, a group of seven uninhabited islands 467 km south of South Island.

A police spokeswoman in Invercargill, a city at the bottom of the South Island, said: "It didn't feel that strong to me: many of the people in the station didn't even feel it."

Japan's Meteorological Agency put the quake's magnitude at 7.4, while Geoscience Australia said it was 7.6.

A spokesman for Geoscience Australia said seismologists were expecting no damage given the distance offshore and might review the magnitude figure.

Volcanic arcs and oceanic trenches partly encircling the Pacific Basin form the so-called Ring of Fire, a zone of frequent earthquakes and volcanic eruptions and the location of the top 10 earthquakes in the world since 1900. All of the top 10 measured an 8.5 magnitude or above.