Christchurch continued to rumble overnight with two further aftershocks following the magnitude 4.9 quake which shook the city at 10.30am yesterday causing shoppers to flee as bricks and mortar crashed from buildings.
Over two dozen smaller quakes have also struck the city since yesterday morning.
The latest aftershocks were a magnitude 4.4 quake at a shallow depth of 3km just after midnight today followed by a magnitude 3.0 aftershock at a depth of 6km at 2am. Both were located close to the centre of Christchurch.
A Christchurch police communications spokesman said there were a few reports of damage.
Acting mayor Ngaire Button said most of the cordons in central Christchurch had been removed following a briefing this morning.
She told Radio New Zealand that Cashel Mall from Colombo St to Oxford Tce would remain closed today after the aftershocks shattered glass.
Police, council staff and engineers would be carrying out assessments throughout the day.
Yesterday's aftershocks were a setback for retailers given Boxing Day sales were so important, Ms Button said.
"It's very difficult for the central city because we've all been working together to try and bring about this recovery. Boxing Day sales are so important for our retailers."
There were no reports of injuries, despite the largest aftershock happening mid-morning on one of the busiest shopping days of the year.
Water, wastewater and stormwater networks were undamaged, but power was knocked out to about 40,000 properties.
Electricity was restored about midday, although some traffic lights were not working properly.
A 65-year-old man was arrested and charged with obstruction and aggravated assault on a police officer after refusing to leave the cordoned area. He was due to appear in court this week. Otherwise, people had taken the disruption in their stride.
"Principally we've had some bricks and glass coming off buildings, and because it's not the middle of the night like the original earthquake we're having to make sure people are safe in the city," Inspector Derek Erasmus said.
Police originally cordoned off two central city blocks bounded by Oxford Tce, Lichfield St, Hereford St and Colombo St while building inspectors assessed the damage. About 20 already quake-affected buildings were of concern.
A Civil Defence Emergency Operations Centre was set up at Christchurch City Council's Hereford St building and emergency services were assessing the situation. No major damage had been reported in the suburbs.
Canterbury and West Coast Regional Rural Fire spokesman Tony Teeling said yesterday morning's earthquake felt very strong and followed a sizeable shake about 2am.
"It was just a different sort of wave, I think. It actually emptied more stuff out in this building that we work in this time than it did last time," he said yesterday.
"The last month's sort of been quiet, you started to forget about it and then suddenly it happens again.
"All the computers and the screens are on their side, and electrical devices like fans and things you have sitting on your desk like printers are all on the floor, and ... it's emptied all the shelving."
Several shops chose to close at Westfield Riccarton, and there was minor damage such as stock on the floor and ceiling tiles falling off. However, the shopping centre was cleared as safe to trade and shops opened again, Westfield spokeswoman Debra McGhie said.
"People are still reeling from a few months ago, and aftershocks keep coming through, which we are monitoring, so there's always a little bit of confusion I think."
Westfield suffered minor, cosmetic damage in the September earthquake which it continued to repair.
"If we were at all concerned for people's welfare being in there we would have activated the evacuation, but we were given the all-clear to continue," she said.
Civil Defence manager Jon Mitchell advised people to follow evacuation advice and to be careful around damaged buildings.
Residents were also advised to contact emergency services only if necessary.
Jolts such as yesterday's were not unexpected and could still happen in the next few months, GNS Science seismologist John Ristau said.
"This is a bit of a wake up call, to kind of say that you can still get large magnitude aftershocks," he said.
