Christchurch is reeling from another shallow aftershock close to the city that caused more damage to buildings, fresh liquefaction and further frayed nerves.
The tremor struck at 11:32am, 10km south-west of Christchurch, at a depth of 9km, GNS Science reports.
A Radio New Zealand reporter in Christchurch says the quake was relatively shallow and strongly felt.
Reports to police and Christchurch City Council include new liquefaction in the suburbs of Halswell and Hoon Hay, and pockets of damage in the city and suburbs.
Bricks fell from a building on the corner of Peterborough and Montreal Streets in the city centre.
A parapet also fell from an already damaged row of shops on Colombo Street in Beckenham, but the council says these were already cordoned off and the parapet fell within the cordon.
A number of work places in the city centre were evacuated but work did continue on demolition of the historic Manchester Courts building - which began on Tuesday morning. That was despite demolition staff being on top of the seven-storey building when the aftershock struck.
Council staff themselves were evacuated from the new civic building but it was given the all clear after about 45 minutes.
The council's building evaluation team received a few requests for both commercial and residential properties to be checked, which the council says is normal after more powerful aftershocks.
Westfield Riccarton shopping centre suffered cosmetic damage, with retailers' stocks also damaged.
Mall spokesperson Deb McGhie says it was evacuated as a precaution only, and there were no major structural damage nor reports of injuries. Ms McGhie says reports of a roof collapse were incorrect.
Mall florist Wendy Wild told Checkpoint ceiling tiles and air vents came down.
A supermarket in the suburb of Bishopdale was also damaged.
Power, phone interruptions
About 10,000 customers lost power in half the city centre and in the suburbs of Sockburn, Heathcote and Lyttelton. Traffic lights also went out in the CBD.
However, power was restored within about 15 minutes.
Telecom, TelstraClear and Vodafone also reported a few problems but these were also resolved quickly
Christchurch Airport, Lyttelton Tunnel and Lyttelton Port stopped operating briefly, while they were checked for damage.
Three hundred staff working on the new terminal at the airport were evacuated.
The tunnel did not suffer any structural damage but lighting and ventilation systems were affected.
New sand lines
Halswell Primary School principal Bruce Topham says liquefaction is clearly visible both in his school grounds and in the road outside.
"It's just a massive sand line going right across the fields. It's the same line as was apparent in the first earthquake."
However, he says road damage does not appear to be anywhere near as significant as the initial quake.
Close to surface
GNS Science seismologist Bill Fry says there have been about 10 aftershocks of this magnitude since the 7.1 earthquake on 4 September, and the reason it was felt strongly was because it was relatively shallow and close to the city centre.
Dr Fry says aftershock sequences can last for months, although the quakes should become less frequent.
Canterbury police district commander, Inspector Dave Cliff, says the vast majority of people coped with the aftershock well.