A 4.8 magnitude aftershock jolted Christchurch on Saturday evening.
It struck at 7.34pm and was centred within 5km of Lyttelton at a depth of 11km.
Radio New Zealand's reporters in Christchurch described the jolt as sharp and violent and lasting for about seven seconds.
They say it caused buildings to rattle.
The aftershock was the biggest of 15 in the Canterbury region on Saturday.
The second biggest measured 4.1 and struck at 10.49am. It was centred 10 kilometres west of Lyttelton at a depth of 5km.
There were 15 aftershocks on Saturday between 5km and 20km from Lyttelton, at depths ranging from 2km and 12km.