There were no reported fatalities. New Zealand's civil defence said 10 people suffered minor injuries in the quakes, with the strongest put at a magnitude of 6.0 at 2.20 pm (0220 gmt) local time.
A series of powerful tremors rattled the quake-prone New Zealand city of Christchurch on Monday, destroying buildings and sending boulders tumbling down hillsides nearly four months after a quake killed 181 people in the city.
There were no reported fatalities. New Zealand's Civil Defence said 10 people suffered minor injuries in the quakes, with the strongest put at a magnitude of 6.0 at 2.20pm (0220 GMT) local time.
Buildings were evacuated and infrastructure damaged across the city, still trying to recover from the February 22 6.3 magnitude earthquake.
Monday's quake knocked the New Zealand dollar lower and was seen as another hurdle to rebuilding New Zealand's second largest city, likely encouraging the Reserve Bank of New Zealand to keep interest rates on hold for longer.
"You can draw a picture already of a significant earthquake," Christchurch mayor Bob Parker told Radio New Zealand. A cloud of dust had enveloped the city after the quakes, he said.
Civil Defence said two people had been rescued from a damaged church. There were no further reports of trapped people.
As with the initial quake, Monday's aftershock sent boulders on the city's Port Hills tumbling towards houses. Parts of the eastern city which suffered the most damage in February's tremor suffered from flooding and liquefaction - where solid ground is turned into liquid by the force of the quake.
New Zealand's GNS Institute said the earthquakes were within the expected pattern after February's tremor and could well trigger fresh seismic activity.
"We would expect a number of aftershocks in the magnitude 4.0 to 5.0 range on the coming days and weeks," said Kelvin Berryman, GNS's manager of Natural Hazards Research.
Prime Minister John Key said the new tremor would probably affect recovery efforts. "I acknowledge that this is a setback for Christchurch, but it does not lessen our resolve to rebuild," he told reporters in parliament.
Power cuts, infrastructure damaged
Power was cut to about 50,000 houses and there were reports of damage to roads, buildings and water supplies.
A number of homes were likely to remain without power overnight, with the temperature likely to dip close to freezing.
Christchurch has experienced a number of strong earthquakes since a magnitude 7.1 quake struck the city on September 4 last year.
On Monday, five tremors of magnitude 4.3 or greater were recorded from 0029 GMT. A 5.5 tremor at 0100 GMT was believed to have caused most of the damage 10km (6 miles) south-east of the city centre at a depth of 11km.
Parts of the city centre have been closed since the February 22 quake. One of the city's tallest buildings, the Grand Chancellor Hotel, has been declared unstable and is being prepared for demolition.
The cost to rebuild Christchurch after the quakes has been estimated at around NZ$15 billion ($12.2 billion).
The Reserve Bank of New Zealand cut rates after the February tremor to a record-equalling low of 2.50 per cent. But signs of recovery and an upbeat assessment from the bank at its review last week have led markets to price in rate rises from December.
However, markets would start to ease back on expectations of a rate hike, said Tim Kelleher, CBA's vice-president of institutional banking and markets.
"It puts things like the rebuild of Christchurch further on delay," he said.
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