Update: Another quake, at least as big as the earlier 5.8, struck the city at 3.18pm and significant aftershocks are still continuing (3.35pm) Some locals are saying the latest was a 6.4.

The USGS gave a figure of 5.8 for the 3.18 earthquake and a depth of 4.9km, located at 43.491°S, 172.844°E. That puts it on land in the west of Pigeon Bay.

Geonet later rated this as a magnitude 6.0 at a depth of 5.8 km, placing it in South New Brighton:

Reference Number	3631380 [View event in Google Maps][View Felt Reports in Google Maps]
Universal Time	December 23 2011 at 2:18
NZ Daylight Time	Friday, December 23 2011 at 3:18 pm
Latitude, Longitude	43.53°S, 172.74°E
Focal Depth	6 km
Richter magnitude	6.0
Region	Canterbury
Location	10 km east of Christchurch 10 km north of Lyttelton

See chart below for all of today’s quakes.

A violent 5.8 earthquake has hit Christchurch at 1.58pm today, followed by a succession of strong aftershocks. No reports of tsunami yet.

RadioNZ has reported one casualty at Eastgate shopping mall and there is liquefaction in St Albans, Wattle drive,  Bromley..

Initial photos of the quake may be found here and there have been rockfalls at Scarborough cliffs.

Christchurch airport has been evacuated, and there is an unconfirmed report that one of the buildings was damaged, some phone networks down, power out in New Brighton.

RadioNZ is saying that the force of the quake is comparable to the devastating 22 February earthquake:

Newstalk ZB reporter Elliott Smith was on the couch in his Mairehau home when it struck.

“It just came and boy, it certainly had a lot of force to it. Judging by the reaction of people, our neighbours have come over, they weren’t expecting anything like this at all,” he says.

Since the quake, Elliott Smith says there’s been several smaller aftershocks which have left people on edge… more here

Qantas flight QF45 Sydney to Christchurch has been diverted to Wellington source

more to come.

Details from Geonet

Reference Number	3631359 [View event in Google Maps] [View Felt Reports in Google Maps]
Universal Time	December 23 2011 at 0:58
NZ Daylight Time	Friday, December 23 2011 at 1:58 pm
Latitude, Longitude	43.49°S, 172.90°E
Focal Depth	8 km
Richter magnitude	5.8
Region	Canterbury
Location	20 km north-east of Lyttelton 20 km north-east of Diamond Harbour 20 km east of Christchurch

Will have been damaging in Christchurch.