Aftershocks continue to rock Canterbury this afternoon after a magnitude 5.0 quake hit late this morning, causing panic, power outages and further damage to some properties.

Power was briefly cut to several areas, while a number of buildings in Christchurch's city centre were evacuated following the 5.0 magnitude shake, which hit at 11.32am and was centred 10km southwest of Christchurch at a depth of 9km.

The quake - another of the large aftershocks continuing to rattle Canterbury since the 7.1 magnitude quake on September 4 - was preceded by two aftershocks this morning and followed by two more, with the latest being a 3.8 magnitude shake, which hit at 1.24pm and was centred 20km southwest of Christchurch at a depth of 5km.

Police had been called to four quake-related incidents, but had not received any reports of injuries, Canterbury district commander Superintendant Dave Cliff told NZPA.

Officers were present at Riccarton Mall, where the building had been partially evacuated after the roof reportedly collapsed in places.

Several bricks had come down from a building on the intersection of Peterborough St and Montreal St in the city.

There were reports of liquefaction in the suburb of Hoon Hay, which council workers were in the process of checking, and a supermarket in Bishopdale had been badly affected, with large amounts of stock falling off shelves.

Landlines and mobile networks in the region suffering from overloading in the wake of the quake.

Telecom reported the 111 service was operational, although some calls were being diverted to Wellington.

No injuries reported

St John Ambulance spokesman Chris Haines told NZPA the service had not been called to any quake-related injuries, but that there had been several panic calls following the aftershock.

Orion general manager of communications Rob Jamieson said about 10,000 Orion customers lost power for up to 20 minutes. Power was cut to half the city centre, the Heathcote area and the suburb of Sockburn.

"The sharp jolt triggered our safety gear and it was just a straight forward matter of switching power back on manually," Mr Jamieson said.

Lyttelton Tunnel was closed, with the quake reportedly having affected its lighting and ventilation system. Lyttelton Port was being checked for damage, but had not been evacuated.

Flights into Christchurch International Airport were delayed immediately following the quake, with one flight from Auckland circling the airport as engineers checked runway for cracks. About 300 workers were evacuated from a construction site at the airport.

The runway and terminal were given full clearance and were operating as normal about an hour after the quake.

Christchurch Hospital suffered some minor damage, including damage to windows and plaster, but all the key buildings had been checked and found to be structurally sound.

The hospital had switched to its emergency generator for a short time, and all services were still running.

Fire services said a number of private fire alarms had been set off by the quake, but there were no reports of fires.

Christchurch resident Shirin Namjou was driving through Avonhead when the aftershock hit.

"My car was being shaken around and the traffic lights were moving side to side. It was one of the strongest ones we have felt."

A Christchurch professional photographer reported that a couple of fresh cracks had appeared in his house, while other residents reported crockery being broken and books falling off selves.

Riccarton's Browsers Garden Cafe owner Flick Holmes said the earthquake was "very scary" and seemed to last about 20 seconds.

"It definitely was a very big one, everything rocked.. just when you think you're getting used to it (another) goes," she said.

Ms Holmes said she was very busy attending to customers, who had been evacuated from nearby Riccarton mall.

'Like a wave'
Herald reporter Jarrod Booker said the earthquake was like a wave travelling through the road.

He said there was initial concern for workers in the Manchester Courts building, which is being prepared for demolition due to damage from the September 4 magnitude 7.1 earthquake.

One resident emailed nzherald.co.nz saying: "Just had a huge aftershock in chch, furniture fell over, things fell off walls and apparently power is out in some areas."

WeatherWatch.co.nz weather analyst Richard Green said the aftershock was the most disturbing one there had been since September 4.

"It was violent and the power has gone off," he said. "My wife who works in the city centre says they have been evacuated and people are clearly scared."

Residents respond on Twitter

Residents took to Twitter to talk about the aftershock, with some initially estimating it was up to 6.0 magnitude on the Richter scale.

"That is the first time the car has danced round the road! Big aftershock... Enough, now time for cafe!," said @AnnieCameron NZ.

"Another big aftershock - people here are a bit shaken. Probably around 6.0 - probably the largest aftershock we should get though...," said @IceNine.

"My office shook big time and cars were jumping in the carpark," Lee Retimana tweeted.

"I'm a little scared."

Donna Robertson described the sounds coming from her house: "My guy and baby were outside, heard it coming and listened to the house creak and the roof squeak, and the water tank next door slosh."

Like many others, she reported no landline or mobile phone coverage. However phone services have since resumed with therhys tweeting: "Power's back on, phone lines up and running & adrenaline still pumping. First big #eqnz in the office."

five15design wrote: "Poor mum & dad were in Countdown when the EQNZ hit, stuff falling down all around them, poor buggers were in the wine section."

The large jolt was followed by a smaller 3.7 quake at 11.41am, 10km east of Diamond Harbour at a depth of 5km.

A 3.8 magnitude aftershock also struck at 1.24pm, 20km south-west of Christchurch at a depth of 5km, according to GNS Science.

- NZHERALD STAFF and NZPA