It is the biggest aftershock in some weeks following the 7.6 quake in the region last month, the New Zealand's Institute of Geological and Nuclear Sciences (GNS) reported.
The quake, hit just before 05:00 a.m. and was centered 120 km west of Tuatapere at a depth of 12 km.
Published 18 August 2009, 03:36 IST