Wellington has been rocked by a severe magnitude-6.5 earthquake this afternoon.
GNS said the quake at 2.31pm, which was only 17km deep, was centred 5km east of Seddon, which is close to the epicentre of last month's big shakes.
Seddon Vineyard manager Garrie Armstrong was on his vineyard when the quake struck.
Asked how the earthquake compared to last month's 6.5 magnitude tremor, he said: "A lot more severe. Obviously a lot shallower. It started off quite gentle and built in intensity. It was quite violent."
Mr Armstrong was not aware of any injuries but said there were reports of considerable damage around Seddon.
"Land slips and stock in supermarkets off the shelves. Broken windows, that sort of thing."
He was now at the local school waiting for parents to collect their children.
The pupils were "pretty good".
"They've been through a bit over the last month."
Federated Farmers Marlborough provincial president Gary Barnett said he was driving just outside of Blenheim when the quake hit.
"It made me stop and think that I had a puncture."
Thousands of Wellington office workers were evacuated from buildings after the initial shake and were milling around on footpaths along Lambton Quay and The Terrace.
Wardens for Unisys House on The Terrace, which was being checked out by Firemen and police told the Herald workers were being allowed in to collect belongings, but were being sent home for the day.
One worker at Bowen State House where the Ministry of Social Development said the shake sent computer monitors crashing to the floor. The building's lifts were out of action until they had been inspected and staff were also being told to go home for the day.
A further significant aftershock struck about 3.10pm, about 45 minutes after the initial shake and fire engines were still racing through the streets of the CBD to call outs.