The 7.8 magnitude tremor caused the southwest of the South Island to move about one foot nearer while the east coast moved less than half an inch, meaning the island actually stretched westwards by roughly 30cm.
Speaking to AFP, seismologist Ken Gledhill, of GNS Science, said the countries remained separated by the 1 400-mile-wide Tasman Sea, but the shift demonstrated the huge force of the tremor, the biggest worldwide so far this year.
“Basically, it’s taken us closer to Australia. The country is deforming all the time because of being on the plate boundary, but this has done it in a few seconds, rather than waiting hundreds of years,” he said.
The quake was powerful enough to generate a small tsunami with a wave of one metre (3ft) recorded on the west coast of New Zealand.
People in coastal areas were advised to move to higher ground for a period of time.
Although it was New Zealand’s biggest earthquake in 78 years, it caused only slight damage to buildings and property when it struck in the remote Fiordland region west of Invercargill last Thursday.
“For a very large earthquake, although it was very widely felt, there were very few areas that were severely shaken,” Dr Gledhill said.
The mayor of Invercargill, Tim Shadbolt, told Radio New Zealand News that he welcomed the fact that parts of the country were now closer to Australia.
“I’m absolutely delighted. I built an international airport in Invercargill because we’re the closest city in New Zealand to Australia and it will become more and more realistic the closer we get,” he said.