A "severe" quake this morning in Cook Strait caused damage and was felt as far away as Auckland.
It also increased the probability of further severe aftershocks, GeoNet seismologist John Ristau said.
The 5.4-magnitude quake struck at 1.07am today, just over a week since a 6.5 magnitude Cook Strait earthquake which caused damage around Wellington.Today's quake was 12km deep and 20km east of Seddon in Cook Strait. It was followed by a swarm of smaller quakes.
More than 1500 people, mainly in the upper South Island and lower North Island, reported feeling the quake.
At least one person reported it caused damage.
''I certainly wouldn't be surprised if this earthquake knocked items off shelves,'' Dr Ristau said. It was also felt in Auckland, Hamilton, and Tauranga.
At midday yesterday, Geonet had downgraded the chance of a 5-5.9 aftershock within 24 hours to 11 per cent. When GeoNet reworked its figures, it would increase the likelihood of a 5-5.9 aftershock, he said.
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