Southland can expect heightened activity from its nearby fault after a severe magnitude 6.2 earthquake this morning, GNS says.
The quake struck just after 1am, and was located 125km west of Tuatapere, Southland, at a depth of 25km.
"This will be related to the subduction zone down there, so the Australian plate is being pushed under the Pacific plate," GNS duty seismologist Caroline Little said.
There would definitely be aftershocks peaking at magnitude five, and there had been several already, she said.
"I'd say most probably there will be heightened activity there for a month or so," Little said.
GeoNet showed there were 181 reports from people who felt the earthquake, from as far away as Wellington.
A Southland police spokesman said there were no reports of any damage or issues overnight.