A "severe" earthquake off the southern coast of the mainland has rattled South Islanders this morning.

GeoNet said the 10km-deep magnitude 6.0 quake struck 160km southwest of Snares Islands at 8.28am.

It comes after Christchurch was struck by a magnitude 5.7 quake on Sunday.

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Twenty three people reported feeling the quake to GNS.

Most of them were in the bottom of the South Island, GNS seismologist John Ristau said.

"It was quite far south of the South Island so it's expected that there wouldn't be too many people who felt it.

"Several of the reports came from people in Invercargill, some were from Stewart Island and we had a couple as far north as Dunedin."

Aftershocks are likely but probably will not be felt, he said.

A store attendant at Stewart Island Gift Shop said the earthquake only felt like "a tiny shake".

"It was just a little one," she said. "We have them all the time. It was nothing out of the ordinary, really."

Nothing fell over in the shop and it didn't have any damage.

The quake was unrelated to Sunday's earthquake in Christchurch.

GNS has recorded 10 aftershocks of the Christchurch quake in the past 24 hours.

"The largest one was just at 2.53am but it was only magnitude 3. They haven't been significant," Mr Ristau said.