Earthquakes were felt in Marlborough and Turangi overnight.
The largest was magnitude 4.5 just after midnight in Marlborough.
GNS says it was centred 30km south of St Arnaud, at a depth of more than 110km.
Two small but shallow earthquakes occurred near Turangi at about the same time. They were magnitude 3.6 and 2.8. Both were at a depth of 4km.