Christchurch has been hit by a magnitude 5.7 earthquake that GeoNet describes as severe.
4.30pm: GeoNet duty seismologist, Anna Kaiser, based in Wellington says seismologists had calculated a 49% chance of an earthquake between magnitude 5 and 5.9 and so today's quake "was certainly a possibility for Christchurch".
Kaiser says the probability of earthquakes greater than magnitude 5 had been dropping since the big quakes in 2010/2011 but seismologists are not surprised by the location of this shake, 15 kilometres off the east coast of Christchurch.
"We've seen plenty of aftershocks located in that area during the earthquake sequence so the location is certainly not a surprise. It's well within the aftershock zone of the Canterbury earthquake sequence."
"We can never predict exactly what's going to happen in the future...typically we see aftershocks that are smaller in magnitude than this current shock.
"Unfortunately people always do need to be prepared."
4.15pm: Scarborough Road has been closed by police after significant rockfall at the nearby Whitewash Head in Sumner.
3.50pm: Just over 500 Orion customers were impacted by the quake but CEO Rob Jamieson says by mid-afternoon the number was down to around 190.
"We are working hard to quickly restore power to those still affected," he says, adding that field crews will carry out their usual checks on Orion buildings and equipment over the coming days, given the magnitude of the earthquake.
3.45pm: Civil Defence is reminding Canterbury residents to check on neighbours, family and friends.
A media spokeswoman says while people will be a bit rattled, it’s important to comfort those who need some support.
She says it’s also important to let Civil Defence know of any damage or people needing assistance.
3.25pm: Christchurch City Council is receiving reports of damage throughout the city and says cliffs have collapsed at Whitewash Heads, Sumner, and also on Wakefield Avenue.
Mayor Lianne Dalziel said that burst watermains are also causing problems in some areas of the city and valves at the city's reservoirs automatically closed. Some pump stations have been affected by power outages and stand-by generators are being brought in to use.
Ms Dalziel says there is general traffic congestion as people attempt to get home, with some traffic signals initially affected.
The Lyttelton Road Tunnel is open, however there is concern about Anzac Bridge, Fitzgerald Twin Bridges and Gladstone Quay and all are being checked.
The council's facilities including libraries closed briefly and some will remain closed until an assessment has been completed.
3.15pm: Canterbury’s District Commander John Price says police, fire and ambulance are out in force to provide reassurance to the community.
He says there are no road closures but there has been some liquefaction and holes that have opened up.
Superintendent Price says there is some minor damage to Palms Mall in Shirley, which has been closed while engineers do an assessment.
3.10pm: The owner of the Ocean Cafe in Scarborough says some people became hysterical as the shaking continued and the cafe "cleared out pretty fast". He says a number of items broke but it's all cleaned up now.
At Scarborough Beach people just stood in the water watching as the dust cloud began to envelop them.
3.00pm: Police say at least 450 homes are without power.
2.45pm: The Fire Service has confirmed there are no reports of significant damage but is urging people to check on their neighbours.
2.25pm: St John has activated its Emergency Operations Centre (EOC) in Christchurch and says that in the immediate post-quake time period there was a sharp increase in calls; mostly related to people with minor injuries from falls as they were running.
Call numbers have now started to return to normal. Ambulance services in Christchurch and Canterbury are operating as normal.
Spark says several cellphone sites are out of action.
2Degrees and Vodafone are not reporting any problems.
2.15pm: Civil Defence Director Sarah Stuart-Black has told ONE News there are no reports of injuries from the quake at this stage.
She says residents should expect aftershocks and be prepared to drop, cover and hold.
Ms Stuart-Black says emergency services are still trying to work out how much damage the quake has caused.
2.05: ONE News sports reporter George Berry says there is minor liquefaction in Bexley, Pines Beach and New Brighton.
The Fire Service has responded to significant rockfall at Whitewash Head.
Flights at Christchurch Airport have not been affected.
1.55pm: No tsunami threat has been issued after the earthquake, but Civil Defence has activated the National Crisis Management Centre in Wellington.
1.50pm: Rebuild Christchurch says that the Riccarton and Northlands malls have been evacuated.
The Fire Service has had no reports of structural damage.
1.40pm: A revised update from GeoNet says the quake struck at a depth of 15km and was located 15km east of the city.
St John has had a number of calls from people who have fallen as a result of the shake, but have had no reports of serious injury or damage.
A number of images have been posted online of dust rising from the Sumner cliffs.
The shake was followed by a light 3.5 magnitude shake at 1.17pm at a depth of 7km.