•A 5.7 magnitude quake struck Christchurch at 1.13pm and was felt as far north as Wellington
•A cliff has collapsed in Sumner
•Shelves have fallen in homes, shops and libraries but so far no reports of serious injuries or damage.
•Riccarton Mall and some other shopping centres have been evacuated.
•Aftershocks are continuing.
READ MORE: Christchurch earthquake - as it happened
A violent earthquake that rocked Canterbury today was a major psychological blow for a region that's still recovering from the tragic 2011 shake that killed 185 people.
Today's magnitude 5.7 jolt, at 1.13pm, was centred 15km east of Christchurch and was felt as far away as Wellington.
Aftershocks continue to hit the city tonight, with a magnitude 4.0 quake at 6.27pm, 15km east of the city.
It was followed by a magnitude 3.5 shake just four minutes later, 10km north-east of the city.
Goods and items fell from shelves in homes, shops and libraries and the Riccarton and Northlands Malls were evacuated.
There was also minor liquefaction in some eastern suburbs, including New Brighton and Parklands.
Christchurch Mayor Lianne Dalziel said water mains burst in several areas, including on Office Rd, the corner of Shirley and Alfred Sts, Hurst Place, Hargood St, Courtfield Close, Hills Rd, Bower Ave and Marriots Rd.
Traffic congestion was heavy in some parts of the city, particularly around Marshland Rd in Sumner.
Some facilities and businesses were closed when the quake struck, including council libraries.
Some buildings remained closed for the rest of the day as damage checks were done.
In Parklands, Linkwater Way - a pot-holed, crumbled and broken road that only on Friday was finally turned back into smooth black asphalt - was again bubbling with sooty grey water.
The street's close-knit residents pitched in with shovels and spades to clear the worst of the liquefaction.
Linkwater Way residents Gary and Tina Bell's backyard swimming pool collapsed during the shaking, sending thousands of litres of water into their home, which is awaiting demolition after extensive damage in the killer magnitude 6.3 quake on February 22, 2011.
"It's a bit of a kick in the guts, to tell you the truth, but that's life - we'll carry on and be 'right'," said Mr Bell.
St John said it had a sharp increase in calls following the earthquake but most related to people suffering minor injuries when they fell while running.
Nathan and Karaan Robinson and sons Murphy, 10, and Charlie, 8, who live in Sumner, were shaken by the event.
"It certainly brings back a lot of memories," Mr Robinson said.
The boys were playing Xbox when it happened. After initially trying to save the TV, they ran outside.
"It was pretty scary," Charlie said.
After checking their house for damage - a painting off the wall and a few dents in floor from fallen objects - they went to Scarborough Beach for milkshakes.
The beach was packed with people who, although shaken by the earthquake, were not put off from having fun on the beautiful sunny day.
Robert Davey and Elaine Smith, with Arianna Smith, 8, were driving to Sumner for a swim when the violent tremor started.
Their car was "rocking", they said, and car alarms went off.
Earthquake Commission chief executive Ian Simpson said people who had suffered damage to their home, contents or land have three months to lodge their claim after taking care of themselves, their families and friends.
"It can take some time for the picture regarding claims to emerge as people come to terms with what's happened and had a chance to take stock of what's happened to their properties," he said.
"EQC senior managers met this afternoon, and we will be monitoring the situation as it unfolds. There have been reports of liquefaction and we have geotechnical engineers out in the field to make an initial assessment of the damage. We are also increasing the number of staff in our contact centres from tomorrow to handle any increase in calls."
Canterbury District Health Board chief executive David Meates there had not been any increase in patient numbers as at 4.30pm but there were reports of minor damage to some board buildings. Further engineering inspections were under way.
Mr Meates said mothers and babies who were in the Burwood Maternity Unit were moved temporarily to other facilities as a precaution while the building was checked.
General practices, pharmacies, after-hours services and the hospital emergency department were operating as normal, with no increase in patient numbers.
Canterbury Earthquake Recovery Minister Gerry Brownlee said there appeared to be some damage to cliffs in the Port Hills, and Land Information New Zealand engineers were surveying the area.
Mr Brownlee said it would be "cold comfort" for people who had already been through 13,000 aftershocks in five years, but a magnitude 5.7 quake was part of the predicted "decay curve" from the 2010 and 2011 tremors.
He said strengthening work done since those quakes meant people could be more confident about the way the built environment responded to a large shake.
The impact on Christchurch residents was more likely to be psychological rather than physical.
"The uncertain bit is just what this does to individuals and how this shakes things up," Mr Brownlee said.
Prime Minister John Key said the people of Christchurch were resilient.
Speaking after being booed off stage at today's Big Gay Out festival in Auckland, he said he was pleased no one had been seriously injured in the violent shake but said it was unfortunate that it came so close to the five-year anniversary of the killer earthquake.
The National Crisis Management Centre was activated after the jolt. It warned Canterbury people to
• Expect aftershocks and remember to drop, cover and hold.
• Look after themselves and get first aid if necessary.
• Help others if they could.
• Assess their home or workplace for damage. If the building appeared unsafe, get everyone out.