The following earthquake has been recorded by GNS Science:

Reference number: 3366146/G
Universal Time: 3 September 2010 at 16:35
NZ Standard Time: Saturday, 4 September 2010 at 4:35 am
Latitude, Longitude: 43.54°S, 172.23°E
Location: 30 km west of Christchurch
Focal depth: 33 km
Richter magnitude: 7.4

Web page: GeoNet – New Zealand Earthquake Report - Sep 4 2010 at 4:35 am (NZST)

Widely felt throughout New Zealand.

Massive 7.4 quake hits South Island - national | Stuff.co.nz