Christchurch dog Teabag, cowering after the quake. Her owner said it took a lot of biscuits and a stuffed caterpillar to get her out again.

Liquefaction in the Christchurch suburb of Hoon Hay, following today's 5.0-magnitude aftershock.

The area where the liquefaction occurred, Hoon Hay, was one of the worst-hit areas in the 7.1 quake.

Resident Alex Mitchell said he returned home 15 minutes after the quake hit and "stuff was still pouring out of the ground".

Liquefaction in the Christchurch suburb of Hoon Hay, following today's 5.0-magnitude aftershock.

A severe aftershock rattled Canterbury this morning, causing power cuts and sparking evacuations in parts of Christchurch.

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Frightened inner-city workers fled their offices after a 5.0 magnitude earthquake rattled already frayed nerves in Canterbury this morning at 11.32am. It struck 10 kilometres south-west of Christchurch at a depth of 9km, GNS Science said.

GNS Science duty seismologist Sara Page said Christchurch residents would have felt the quake more strongly because it was a lot closer to the city than previous aftershocks.



"Some of the shocks have been 20km away - that would be the biggest, closest one we've had for a while," Page said.

"It was only 10km away and it was quite shallow too."

GNS said today Canterbury residents could still be experiencing aftershocks a year from now.

Frazzled nerves were further strained when a 3.8 magnitude aftershock struck at 1.24pm, less than half an hour after many evauated offices and shops in the central city had reopened. It was a shallow quake centred 20km south west of Christchurch at a depth of 5km.

Page said before the 7.1 Christchurch quake, a magnitude 5.0 would have been considered a large quake for New Zealand.



She said although the jolts were of a significant size, they would be continued to be called "aftershocks" until the level of seismic activity in the area returned to what it was before the 7.1 quake.

'LIFE CHANGING EXPERIENCE'

The aftershock gave two workers suspended above Christ Church Cathedral "a life changing experience'' this morning.

Ben West of Stoneworks and John Hare of Holmes Consulting were suspended from a crane on a platform inspecting a stone cross on the southern gable of the cathedral when the aftershock struck.

Hare hung onto the stone cross as it swayed back and forth, while West gripped onto the stone gable.

"We just shared a life changing experience, that was all,'' quipped Hare.

West and Paul Cullinane of Stoneworks (pictured) later removed the large stone cross, which had been deemed unsafe even before the aftershock struck.

Watch video of earthquake shaking Halswell Superliquor in Christchurch today:

POWER CUT

Orion commercial general manager Rob Jamieson said 10,000 customers in the CBD, Heathcote and Sockburn were without power for 15 minutes following the quake.

Power transformers automatically shut down and had to be manually restarted. Christchurch Hospital reverted to back-up generators during the outage. Mobile phone networks were reported to be overloaded.

The Lyttelton Tunnel has reopened after it was closed for about two hours following the 5.0 aftershock, New Zealand Transport Agency area manager Barry Stratton said.

Police said initial indications were that there had not been any significant damage, although some phones had been affected.

RESIDENTS RUN FOR COVER

Fiona Fidow at the Cupcake Collection in Westfield Mall, Riccarton, said it was the second biggest shock they had felt since the original quake.



"This was very loud, very strong shaking. All our china is smashed in our kiosk. The mall alarms are going off and the mall has been evacuated. Quite a few people are crying and hysterical. There are a lot of frightened people."

The mall was evacuated, but reports parts of the roof were collapsing were not correct, Westfield said. It has since reopened.

Christchurch resident Sean Scanlon said it felt like it was well over magnitude five.



"The house was rattling and books fell off the shelves."



His wife, Lucy Scanlon, had been forced to take cover under her desk at work in central Christchurch.

Radio New Zealand reported that Lyttelton wharf had been evacuated.

The school closest to the aftershock's epicentre, Tai Tapu, "got off lightly'', with no noticeable damage, said principal Graeme Trist.

Phone lines were down for about 30 minutes at the school, but power was uninterrupted.

"The building shook vigorously and the children all got under their desks,'' Trist said.

"But everything and everyone is OK and everything will carry on as normal this afternoon.

"It seemed to have all the hallmarks of the original one [on September 4], but it did not go on as long.''

FRESH LIQUEFACTION

Halswell School principal Bruce Topham said the only new damage he discovered was more liquefaction, which had come out of a crack ripped through the field in the September 4 quake. Staff and pupils were all OK, he said.

The aftershock has caused more liquefaction in the suburb of Hoon Hay, one of the worst-hit areas in the 7.1 quake.



Resident Alex Mitchell said he returned home 15 minutes after the quake hit and "stuff was still pouring out of the ground".

"It's exploded everywhere. If we'd been home at the time we could have got some really impressive pictures," he said.

Four other quakes this morning preceded the 5.0 tremor. A 4.0 magnitude quake struck at 10.54am, 20km south-west of Christchurch.

A 3.3 quake hit 10km west of Kaiapoi at 9.43am, a 2.8 hit 10km east of Darfield at 7.48am, and another 2.8 hit 10km south of Christchurch at 3.19am.

Minutes after the 5.0, a magnitude 3.7 quake struck 10km east of Diamond Harbour at 11.41am.

Frazzled nerves were further strained when a 3.8 magnitude aftershock struck at 1.24pm, less than half an hour after many evacuated offices and shops in the central city had reopened. It was a shallow quake centred 20km south west of Christchurch at a depth of 5km.

GNS Science said the 5.0 earthquake fell within the expected number and size of aftershocks. It said up to 5.0 magnitude or greater quakes could be expected. It was the third earthquake of that size since October 4.

PLANES GROUNDED

Planes were grounded at Christchurch Airport, and those in the air were in holding patterns while engineers checked the runways for damage.



About 300 workers were evacuated from a construction site at the airport.



A spokersperson from the airport said flights were set to resume.

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