LATEST: Marlborough bore the brunt of a rattling 6.6 quake that also caused havoc on Wellington roads and was felt throughout much of New Zealand today.
There were no reported deaths or major injuries suffered in the quake that hit at 2.31pm or the aftershocks that followed - many of them greater than magnitude 5, including a 6.0 about three hours after the 6.6.
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Today's shakes have mainly been centred around the small Marlborough town of Seddon, which has been at the centre of seismic activity since a magnitude 6.5 quake on July 21.
Children in the Seddon School hall screamed when the 6.6 struck. Paige Jackson, 9, said she was lying on top of other children and a light fell on them.
A Marlborough Civil Defence spokesman said a welfare base had been set up at Seddon School for people who couldn't return to their houses tonight. Residents could go there if they were unsure what to do.
There were widespread power cuts in Marlborough and buildings evacuated in Blenheim.
Wairau Hospital's emergency department in Blenheim said two people were treated for minor injuries because of the quakes.
The staff and patients were shaken but there were no reports of major damage, the hospital said.
Seismologists warned the aftershocks would continue. Duty seismologist Anna Kaiser said the 6.6 was bigger than the July 21 quake and was centred 30 kilometres south-west of that one.
"This one occurred on land whereas the previous one was over water. It is closer to the town of Seddon," she said.
Today's 6.6-magnitude earthquake was the same kind of quake as last month's 6.5 event and was not what would usually be expected, GNS Science said.
The two were termed a doublet.
GNS Science duty seismologist Caroline Little said it was somewhat unusual to have had the 6.6 quake today as the odds had been against an earthquake of that size - but it had still been a possibility.
In the 3.5 hours after today's 6.6 quake there were at least 77 aftershocks, of which 11 were above magnitude 5.
"This is just the stresses in the crust realigning back to an equilibrium," she said.
The initial 5.7 quake on July 19 had changed the stresses the Marlborough fault region was under.
"The faults were quite highly stressed to begin with and so the first earthquake tipped them over the edge and caused them to rupture. It's like a domino effect."
The 5.7 had been on a different fault from the subsequent quakes. It had been deeper and the fault had moved differently.
It was not known yet whether the 6.5 quake on July 21 and today's 6.6 and 6-magnitude quakes had been on different parts of the same fault or on different faults, Little said.
Shortly before the 6-magnitude quake it had been calculated there was a 38 per cent chance of a 6 or greater in the following seven days, and 28 per cent in the next 24 hours. In the 24 hours from 5.30pm it had been calculated there would be an average of 31 quakes between magnitude 4 and 4.9, based on previous earthquakes in this country and around the world.
Between zero and seven quakes of magnitude 5 to 5.9 had been expected, while from zero to two quakes of magnitude 6 or greater had been expected, and one had struck.
Marlborough Civil Defence incident controller Chris Hayles said tonight it was a case of "hurry up and wait" as help gathered at the welfare centre in Seddon.
The priority was checking everyone was safe and encouraging them to gather at the centre in the Seddon School hall, he said tonight as strong quakes continued to rock the area.
His biggest concern was a forecast for 150mm of rain before Sunday.
At first light, the Emergency Operations Centre in Blenheim would stock-take what help was needed to weather-proof homes with damaged roofs and broken windows. Businesses had donated materials, including PlaceMakers which offered plasterboard and trucking companies which had contributed tarpaulins, Mr Hayles said.
Builders, building inspectors and plumbers could be called in.
This was not a Civil Defence emergency but the organisation was playing a leading role in welfare, he said.
"I am the eyes and ears on the ground, with the Red Cross helping."
The biggest message was for people to use the welfare centre or it would close.
Twenty-two people will be spending the night at the emergency centre.
Thirty-three people have registered with Civil Defence, advising they will not be returning to their homes tonight although some of them have made their own arrangements for accommodation.
Search and rescue teams have continued to check properties tonight, checking property damage and making people aware of the emergency centre.
Two people were reported to have required medical attention after the quakes, although both were medical problems rather than injuries.
The majority of the houses in Seddon had sustained some degree of damage but most are still habitable, a spokesman said.
State Highway 1 remains closed tonight between Blenheim and Kaikoura.
Roads are still dangerous and driving is not advised, particularly during darkness. The rail bridge in Seddon, for example, has slumped.
Marlborough District Council staff and Civil Defence team members will go to Seddon early tomorrow morning to begin assessing damage and assessing any welfare needs.
Power was restored to all but about 100 customers in the region tonight.
Hayles said community support had been huge.
People were recognising the welfare centre was the best place to be, in a group. Rural Fire Brigade volunteers barbecued sausages for evacuees and the Salvation Army delivered meals.
Electricity in the Seddon district was patchy tonight with power out around the Blind River area near the epicentre where homes were badly damaged, roads were cracked and covered with rocks and bridges approaches were out.
In Blenheim, buildings were evacuated, Stadium 2000 and the public library among them. Blenheim police cordoned off the Forum in the central township and sent all shop owners and staff home after large cracks that appeared on a pedestrian flyover.
Police were checking for damaged buildings, and to ensure people were safe. Most Blenheim businesses closed.
Staff at the three Countdown supermarkets in Blenheim managed to keep customers calm as stock fell off shelves around them and then evacuated the buildings.
Countdown spokeswoman Kate Porter said the buildings had been checked through a company protocol, including structural checks, before the staff were allowed back in to clean up the mess.
Photographs taken at the Redwoodtown supermarket showed considerable damaged in the aisle. However, Ms Porter said the mess was cleared away and all three supermarkets reopened by 6pm.
The Fresh Choice supermarket at Picton was also open, but the Supervalue supermarket in Seddon remained closed.
Wineries at Riverlands Industrial Estate and Cloudy Bay Industrial Estate, south of Blenheim have sustained damage, but to what extent is unclear.
South Pacific Cellars winery manager Graeme Paul said all staff were safe, but a wine cellar and several tanks of wine had sustained "significant damage".
"There are tanks everywhere," he said. "Several tanks have ruptured and there is some wine loss"
The building was too dangerous to enter, and he had sent staff home for the night, he said.
"It’s pretty dodgy in there."
The volume of wine lost was unknown.
Saint Clair Family Estate senior winemaker Hamish Clark said one of their 300,000 litre tanks holding 2013 sauvignon blanc had ruptured.
They had managed to save most of the wine by pumping it into spare tanks, but the loss of wine would probably be in the ‘‘thousands of litres’’, he said.
Pernod Ricard’s Fabian Partigliani said their Marlborough winery and vineyards did not appear to have been damaged, but would follow up with more detailed inspections.
Edith and Ian McGhee moved to Seddon to escape the earthquakes in Christchurch and after today's shake are feeling like they've "been there, done that".
"These one's were as bad as Christchurch as far as we're concerned," Mr McGhee said.
"The severity was the same," Mrs McGhee added. "I was trying to get outside and the walls and everything were disappearing around me; it usually takes me three seconds to get outside but today it was a bit longer."
Schools around the Wellington and Marlborough regions were reporting minor damage to buildings such as broken glass, the Ministry of Education said.
All school buildings in affected areas would be assessed by engineers "as a priority", ministry spokesman Matt Radley said. Schools not cleared for use on Monday would be listed on the ministry's website, he said.
The ministry had also closed its offices in Marlborough, Nelson, Wellington, the Hutt Valley and Wairarapa, until engineering assessments cleared them.
Wellington Mayor Celia Wade-Brown arrived at the regional civil defence headquarters on her bike shortly after the quake.
"[The earthquake] was very strongly felt there; I have to say I was probably the second person down on my hands and knees and then got reports from [civil defence] that there didn't appear to be significant damage and I said I'd come down here. On the way I stopped and where the lift shaft in the carpark's been propped up, police have just cordoned that off for the moment as a precautionary measure."
She reported that Wellington's traffic system had been "chaos", with roads leading to major highways gridlocked.
The situation was compounded by the cancellation of all rail services. Hundreds of people were stranded at Wellington Railway Station. The city's airport remained open after a brief runway inspection.
Civil Defence controller Bruce Pepperrell said the quake was felt strongly in Wellington and Kapiti, but there were only minimal reports of damage.
"There has been the occasional fire, a little tiny bit of facade damage but nothing much to speak of. The big damage is in people's confidence at this stage."
It was probably a blessing that people had been about to head off home for the weekend.
A lift shaft in Lukes Lane that was damaged in the July quake will now have to be demolished. Contractors would begin demolition tonight or tomorrow morning.
The priority was assessing buildings for cumulative damage from the various quakes. There was a concern about this series of earthquakes coming on top of the previous series.
Telecommunications provider Telecom NZ said there did not appear to be any significant damage to its networks in the lower North Island and Upper South Island after the earthquakes.
The earthquake triggered severe congestion across the networks. The 111 service remained operational, although traffic normally routed through the Wellington call centre had been diverted to Christchurch.
While the initial congestion had abated, Telecom NZ was encouraging customers to use text messaging rather than calling to reduce the congestion and to help keep lines free for emergency calls.
Further north, a series of quakes, including some centred in the Rangitikei region, cut power to Hunterville.
THE CITY GROANED
On Wellington's waterfront, cranes swayed and the city seemed to groan.
Joggers stopped in their tracks and struggled to stand. Amanda Beeslaar, a visitor from Auckland, said the quake was ''terrifying''.
''It felt like a jet plane coming over and then it just started shaking. I thought the earth was going to open up.''
Sam Stanley was in the NZX building when the quake hit.
''I feel a bit queasy, it was swaying so much. I waited about ten seconds and got under my table, then we decided to get out.''
Shoppers ran from Karori Mall when one massive shake cut off the power, which has since been restored.
''I was in the Salvation Army store and I didn't realise how big it was at first,'' one teenage shopper told Fairfax Media.
"No one really realised it was happening and then there was one really big shake and the power went off,'' Tess Norquay said.
''One woman yelled an urgent 'get out, get out'."
There were hundreds of ''felt it'' reports on the Geonet website, including reports as far south as Dunedin and as far north as Auckland.
Karori resident John Nimmo, 81, said that he thought the quake had been worse than the July 21 quake, which measured 6.5.
''It shook the hell out of this house,'' he said.
''I felt it was far worse than the previous big shake, but I was upstairs when it struck.''
His daughter-in-law Anne-Marie, who called to see if he was okay, had been working at a pharmacy in the mall.
It had cleared out the customers and closed, as had the two supermarkets in the mall. Karori Pool had closed initially, but it had reopened about half an hour after the shake.
Children at Karori Normal School had dived under their desks, and some were crying Year 5 student Ben Moore told Fairfax Media.
''It was really scary, I ran under the desk,'' Ben said.
''Kids were upset, there were a few kids crying.''
The Seddon area has been the centre of seismic activity since the day before a magnitude 6.5 quake struck on July 21.
GNS Science seismologist Stephen Bannister said that quake had released energy equivalent to 100 nuclear bombs of the size released on Hiroshima.
"If it had been under the city we would have been looking at equal damage or close to what happened in Christchurch."
There have been hundreds aftershocks since then.
They continued to rumble in Seddon last night, with a magnitude 4.4 earthquake shaking the area at 7pm.
It was quickly followed by a magnitude 2.4 and magnitude 3 in the same spot.
Within half an hour of the major quake, a shallow 4.2 magnitude earthquake shook Hunterville, followed by ones near Turangi and Ohakune.
Then at 3.09pm, a "severe" quake hit north of Taihape.
It was a 4.9 magnitude earthquake at a depth of 13km, Geonet said. A further aftershock was reported by Geonet near Levin at 3.27pm.
The 4.5 magnitude shake was centered 10km north-east of the Horowhenua at a depth of 29km.