Geonet reported the epicentre of the quake was centred 15km east of Christchurch at a depth of 15km.
A cliff collapsed at Whitewash Head near Sumner and engineers are assessing it to establish its stability.
There are reports of liquefaction and flooding in parts of New Brighton.
There have been only minor injuries reported.
All public transport is running as normal. The public was initially asked to avoid the Sumner area but cordons have been lifted.
Lyttelton Tunnel has been checked and is open.
Civil Defence has activated its national crisis management centre.
Power and water
Power has been cut to 500 homes mainly in the north-east of Christchurch. A further 100 are without power at Banks Peninsula.
Water mains have burst in Office Road, on the corner of Shirley and Alfred streets, Hurst Place, Hargood Street, Courtfield Close, Hills Road, Bower Avenue, and Marriots Road.
Teams are checking on the situation and people are being asked to drive with care in those areas.
St John had a spike in calls but are now operating as normal and said people should call 111 for emergencies.
St John is encouraging people to check on their neighbours, friends and family, particularly those who are elderly, ill or live alone.
Anyone who has queries about non-urgent injuries or health issues can call Healthline on 0800 611 116 for free advice from registered nurses.
All Burwood Hospital systems are running and the only damage appears to have affected its water and sewage systems.
The Ministry of Education is telling Christchurch people to check their school's Facebook page to see if they will open tomorrow.
The ministry said at this stage Christchurch Girls' High School was the only school to indicate it would not be opening tomorrow.
Christchurch Girls' High principal Pauline Duthie said the school had a protocol in place that it did not open following an earthquake of higher than 5.5 magnitude until the buildings had been checked by a structural engineer. That will be done tomorrow and all going well the school will reopen on Tuesday.
Several hundred staff and students have been evacuated from the University of Canterbury's campus in Christchurch, though there has been no reports of damage.