A second strong aftershock in Christchurch this morning left frightened city workers hugging each other in support and saw tourists flee Christchurch Cathedral.
The latest 3.9 magnitude quake struck at 11.10am, 10km east of Christchurch, and five kilometres deep.
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This morning's initial 5.1 quake was centred 10km southwest of Christchurch at a depth of 10km at 6.03am.
It was followed by a magnitude 3.4 tremor recorded at 8.02am, 10km underground, 10km southwest of the city, and a magnitude 4 quake recorded at 8.06am, 15km deep, 20km to the west.
An accountant on the 12th floor of the Price Waterhouse Coopers building in the CBD said staff were hugging each other in support after 11.10am aftershock.
Julia Taylor said: "It was quite scary and you would think I would be used to them by now."
She said she did not usually feel small aftershocks but the earthquake-secure building was left swaying after the recent shock.
An Australian tourist who was in the Christchurch Cathedral when the aftershock struck said she thought the building was going to fall down.
Sharon Muir, from New South Wales, said she was shocked at how calm the other people around her appeared after the quake.
"I guess you guys must be used to them by now because everyone else was so calm except me," she said.
Antonino Maltese, from Sydney, was also in the Church and said he ran out when it started shaking.
"I have never experienced an earthquake before and I was scared so I ran out of the building when I heard it moving," he said.
Maltese is looking forward to returning to Australia and telling his family and friends how he experienced an earthquake in Christchurch city.
Christchurch resident Sean Scanlon described the latest quake as a "bloody good, short, sharp jolt".
He said it felt worse than the 5.1 quake.
"I had a friend visiting and we looked at each other and jumped under a doorway. Stuff leapt off the shelves and bookcases."
St John spokesman Ian Henderson said the ambulance service had seen a slight increase in people calling because of chest pains, reporting that they "felt unwell"' or "sick", and general symptoms of anxiety following this morning's first quake.
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GNS Science duty seismologist John Ristau said the 5.1 magnitude aftershock did not cause as much damage as the 4.9 Boxing Day quake because its epicentre was deeper and further away from the city.
He said an end to aftershocks was not in sight for Christchurch.
"Aftershocks will go on for months, even maybe a year," he told Radio New Zealand, while GNS Science warned Canterbury residents they should prepare for a sizeable aftershock about every four to six weeks.
The 5.1-magnitude tremor was the eighth-biggest shake since the 7.1 earthquake in September, according to the Quake Live site.
More than 900 people reported having felt the initial quake, including from as far away as Greymouth and Dunedin, with 13 reports of slight damage around suburban Christchurch and one report of damage in Kaiapoi, 19km north, GNS Science said.
Rolleston resident Amanda Rait said she woke to her whole house shaking.
"It went on for a good 15 seconds and everything was moving. I could feel it not only around me but underneath me as well," she said.
Rait did not feel the Boxing Day aftershocks and said this morning's 5.1 quake was the biggest she had felt since September 4.
"When we were shaking it was bringing back memories of how the first one started," she said.
Vince and Kim Thompson from the suburb of Redwood said the quake woke them and their five children with a "hell of a fright".
"Wow! That was a mean way to wake up here... the shaking seemed to keep going and going! Not very nice."
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Roofing contractor Tony Stuart awoke today wondering how much more damage his house could absorb in the "shake rattle and roll" of the 5.1 tremor.
Stuart, who lives in the Cashmere Hills, said "the whole house was shaking on its foundations".
"The whole house just shakes like a dog with a bone. The whole house just shakes, rattles and rolls."
He said this morning's first aftershock lasted about 15 seconds.
"I've had enough of them, I am sick and tired of them."
He said he was noticing more damage in his house all the time.
"It is amazing... the violence and how bad a house can shake. It's the noise and everything shakes and rattles and you wonder what sort of force causes this."
He said many people were starting to think the aftershocks might be over "when bang, you get hit by another bugger. Nerve ends are getting very frayed".
Stuart said he had barely stopped repairing roofs and chimneys since the big 7.1 magnitude earthquake of September 4 and said today's first aftershock caused more damage to chimneys.
Many chimneys were removed after the September earthquake to just below the roofline but with thousands of aftershocks, that was not enough, he said.
"Yesterday I had a guy ringing who wanted his chimney taken down further in case another big quake comes. He is a day too late."
He said chimneys could still be damaged below the roof level and bricks could still be in danger of coming through the ceilings.
Meanwhile in Rangiora, Jan Reed said she had no water at her house from 6am to 7.30am due to the first quake.
Christchurch police said no new cordons had been established. They had not received any calls from the public about damage in the city.
A Fire Service spokesman said there were no reports of damage as yet, but they would probably start getting calls about chimneys soon.
"It was fairly big - bigger than the Boxing Day one," he said.
- The Press with Stuff and NZPA