Christchurch residents received a series of shocks overnnight, including a 5.3 magnitude quake rocking the region at 10.34pm.
The main jolt, centred 10km west of Akaroa, was felt widely across Canterbury although there were no reports of significant damage.
Police said power was out in small pockets around Avonhead and Ilam and "alarms are going off everywhere", a spokesman said.
Mayor Bob Parker, on his Facebook page, said the city should expect a few more "tremblers".
The region was rocked by a further 10 aftershocks overnight, with the biggest being a magnitude 4.4 shortly before 3.30am.
GNS Science duty seismologist John Ristau said it appeared another small fault below Banks Peninsula had ruptured, causing the sharply felt magnitude 5.3 quake.
She Who Must Be Obeyed in still down in Christchurch; we haven't rung yet, and we hope she's catching up on some of the shut-eye that she will have missed in the early hours of this morning when aftershocks were coming with some considerable frequency. We had a txt exchange after the 5.3 though.
The main aftershock was out Akaroa way; Gravedodger's territory. We hope that he and his good lady, Tinman, Lindsay Addie, GPT1 and other Canterbury-based commenters here at Keeping Stock are ok this morning; our thoughts are with you all.
UPDATE: SWMBO is safe and well, albeit sleep-deprived.