The aftershock was one of thousands which have struck the region since September 4's magnitude 7.1 quake, and which experts warn could continue for some time.
Today's struck at 1.34am at a depth of 7km and was centred 20km west of Christchurch.
GNS Science said the quake was widely felt and possibly caused damage.
However Christchurch police and the region's fire service told NZPA there had been no reports of damage.
The aftershock followed a 3.8 magnitude quake which struck at 12.12am.
