The quake shook the battered city at 5.49pm and was followed overnight by several smaller aftershocks, the largest of which was a magnitude-4.1.
The 5.3 aftershock was among the largest to hit the city since the tremor on February 22.
Civil Defence authorities said the Strategy Building, on the corner of Montreal, Victoria and Salisbury Sts, had become too dangerous to remain standing.
Demolition began yesterday afternoon and was expected to take up to a week. Nearby roads were closed to the public.
Some houses in the Lyttelton, Redcliff, Mt Pleasant and Estuary Rd areas were without water after 12 water pipes burst, but repairs were expected to be completed yesterday.
Overall, water and storm-water systems were working normally and power, which was initially cut to 20,000 homes, had been fully restored within three hours, Civil Defence said.
Small pockets of liquefaction had been reported in the eastern suburbs and rocks which fell on to Evans Pass Rd had been cleared.
Engineers were in the central city yesterday to assess any further damage caused by the aftershock. Until the assessment was completed, there would be no access for business owners to the red zone.
The Earthquake Commission (EQC) yesterday said assessments of quake-related claims were on track, with more than 5000 homes inspected by both an assessor and a builder.
"It's vital for people with claims that we spend time at their properties to get a thorough view of the damage," EQC chief executive Ian Simpson said.
"Our assessments are currently focusing on properties with severe structural damage and we are on track to complete all the EQC claims assessments by mid-December."
Mr Simpson said 4500 priority winter heating repairs were expected to be completed by mid-May.
"The clean heat hub has made 25,000 calls to identify those people in most need. These include people who are at additional risk with the onset of winter, including the sick, elderly or those with other special needs."
About 6000 other urgent repair projects were under way.
EQC has received 294,618 claims for earthquake damage since the 7.1 magnitude tremor on September 4 last year, including 110,294 claims for the February 22 quake.
Nearly $829 million has been paid to date, Mr Simpson said.
Saturday's big aftershock was centred within 5km of Lyttelton, 12km southeast of central Christchurch, at a depth of 11km, GNS reported.
Christchurch remains devastated following the February quake, which claimed an estimated 181 lives.
• A deep magnitude 5 earthquake struck south Waikato on Saturday evening.
GNS Science said the 190km-deep quake struck 10km east of Tokoroa, roughly midway between Hamilton and Taupo, at 11.15pm.
• A magnitude 4.4 earthquake rattled the lower South Island yesterday afternoon.
The 2.48pm tremor was centred 140km southwest of Te Anau at a depth of 15km, GNS Science reported.
