http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=10671049more of a running timeline of updates:
http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=106710507.49
Police have just issued a warning to "criminals" after reports of looting, some in Colombo St.
"Do not attempt to take advantage of this," said Detective Sueprintendent Dave Cliff.
Police have sealed off part of the Christchurch CBD due to the level of damage sustained by the buildings.
7.40am
Herald reporter, Jarrod Booker, on the scene in Christchurch has just filed an amazing interview with resident, Knee Doherty
"We didn't even notice the movement as much as the noise. The back of the house is pretty much gone. All the house next door is gone. It was just a massive noise."
7.37am
Herald reader, Terry Whiting, tells nzherald.co.nz:
"Our son in Christchurch says that all their furniture is lying on the floor,TV fallen of stand,pc on the floor,and they are sitting in their car,petrified,hoping for assistance."
7.30am
In an interview with NewstalkZB Mayor Bob Parker described the quake as "sharp, severe and terrifying."
7.27am
Mayor Bob Parker has just warned residents to conserve water after fears the water infrastructure of Christchurch may have been affected by the 7.4m magnitude earthquake.
He has told residents not to flush the toilet and to conserve water.
There are fears the sewerage system may have been damaged.
Engineers are checking the City infrastructure now.
7.19am
Civil Defence has activated its national emergency response centre.
7.12am
Christchurch mayor Bob Parker and police have asked people to stay off the roads after reports emerging of damage to the roading network around Christchurch.
Engineers will check the bridges on the Christchurch motorway network for damage after the 7.4 magnitude earthquake hit the city.
There are also concerns about some bridges around the city.
7.11am
Herald reader, Gayle Temple, sent us this eye witness account from the earthquake zone.
"We live in Ashburton and were woken to our house shaking and rolling.
"I have never been so scared in my life running from upstairs to get down where we hid under a table. We didn't know what to do having never experiencing anything like this in our lives the after shocks are still happening and I am still shaking.
"Lots of alarms were going off but no damage to our property or those around that we can see."
7.02am
Herald reader, Tony Metternich, reports feeling the quake as far away as Invercargill. It "was two minutes of swaying".
6.37am
Calls are flooding into the police communications centres around New Zealand, causing problems for staff trying to deal with the massive earthquake and aftershocks which have hit Christchurch and Canterbury.
A police spokesman asked residents to call police emergency numbers only in an emergency.
6.32am
Orion power company is working to restore power after the massive 7.4 magnitude earthquake hit Christchurch knocked out electricity.
A spokesperson for Orion said it appeared parts of rural Canterbury and Christchurch were without power.
Orion has asked residents not to call in about the power since its lines are now jammed.
6.20am
Dr Mark Quigley is a lecturer in the Department of Geological Sciences at the University of Canterbury in Christchurch. He has just reported that witnesses told him the Avon River in Avonside overflowed its banks in places due to a surge in the river caused by the massive earthquake which hit Christhchurch at 4.30am today.
He said there are cracks in parts of the roads and gardens around Avonside measuring 20cms across and up to 1 metre deep.
Dr Quigley told RadioLive that the force of the quake had pushed up sand and dirt in mounds in parts of Avonside.
He will post pictures of the quake - when internet connectivity is restored to the city - on his website here.
6.11am
There are some power lines partially down on Avonside Drive, Christchurch.
6.10am
Civil Defence officials and officers from Christchurch City Council are meeting now to determine priorities after reports of damage around Christchurch caused by a 7.4 magnitude earthquake.
6.09am
First pictures are beginning to emerge from earthquake-hit Christhcurch.
This picture is currently being retweeted on twitter, apparently showing damage in central Christchurch.
Click here
6.01am
Students are gathering in the main carpark of Canterbury University after being buffeted by the 7.4 magnitude earthquake which hit Christchurch at 4.30am today, followed by a series of aftershocks.
A student reported that there were no injuries he could see and the University buildings appeared to have not sustained major damage.
6.00am
Police have announced they are investigating a possible case of looting on Colombo St after Christchurch was rocked by a 7.4 magnitude earthquake, but said they have no further details.
5.59am
Darfield, west of Christchurch and close to the epicentre of the earthquake, is experiencing rumbling earthquakes. Power is off in the town but a resident reported only minor damage after the quake, measured 7.4 on the Richter scale, hit at 4.30am.
5.57am
A series of substantial aftershocks is still continuing to rock parts of Canterbury.
A resident in Ashburton reports a major shock hit around 5.50am. However, the town continues to have lighting and power.
"We mainly had stuff knocked off shelves."
5.42am
There are reports of some buildings demolished in Victoria St, Christchurch after the magnitude 7.4 earthquake struck Christchurch and Canterbury.
Police have just asked residents to not travel into the CBD, saying that the older buildings in the central city have sustained damage and they are unsure if any further collapses may occur.
5.41
Reports of the earthquake are coming in from as far afield as New Plymouth and Invercargill.
The quake was centred 33km west of Christchurch but New Zealand residents are reporting feeling the earthquake or aftershocks hundreds of kilometers away.
Have you seen or heard anything? Alert the Herald.