LATEST: A magnitude 5.3 earthquake hit Christchurch at 5:49pm this evening.
The jolt was centred 10km north-east of Diamond Harbour at a depth of 11km.
It cut power to about 20,000 Canterbury homes and weakened at least one building in the city centre.
Christchurch Eastern suburbs also suffered from liquefaction and flooding.
Civil Defence reported that the Strategy Building in Victoria Street was now leaning due to the latest aftershock.
Police cordons have been put up around Montreal and Cashel Streets.
Orion have confirmed power has been restored to Christchurch residents.
The aftershock was followed by a magnitude 3.4 at 5:59pm at a depth of 8km and within 5km of Lyttelton.
Dixie McGregor, who works at the Pegasus Arms on Oxford Tce said emergency services had been mobilised.
"We've got a pub full of people but it's OK here but all I can see outside is the Army and police. Some ambulances have left the hospital too - here we go again."
Comments on social networking site Facebook include, "Is everyone OK? I don't know how much more of this my nerves can take."
One Twitter user said, "TV fell down in that one but it's still going so everything is fine!"
At least 100 'felt it' reports have been recorded on GNS Science.
Press reporter Martin van Beynen, who lives in Diamond Harbour, said the shaking of his weatherboard house was the most violent since the February 22 earthquake.
"We had just picked up our daughter Ella from the airport. She is at school in Auckland because of the earthquake. What a welcome home.''
Kirk Hargreaves, also in Diamond Harbour, said the shaking was as bad as anything he had felt since the February quake.
"My 10-year-old daughter, who was at school in Lyttelton on February 22, and I rushed for the door jamb. She was a bit freaked out.''
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- Fairfax Media