The quake beneath the ocean was estimated at a depth of 10 kilometres, more than 475 kilometres south of the mainland, the United States Geological Survey said.
No tsunami threat was issued.
"Based on the information we have there could be light to moderate shaking in the southern South Island," said Geoscience Australia duty seismologist Greg Breen.
"But no damage is expected."
Several Twitter users in Invercargill and Dunedin said they felt some movement. But a Fire and Emergency New Zealand spokesman told the stuff.Co.Nz news website they had received "not one call for help".
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