A Te Ānau worker described seeing cars "rolling around in the carpark" when a magnitude 6 earthquake struck the lower South Island this morning.
The moderate quake - centred 40km west of Milford Sound in Fiordland at a depth of 5km at 10.20am - was widely felt across the South Island and into the lower North Island.
Te Ānau Helicopters employee Helen Archer said she and another worker at the site were still feeling "sea-sick" after what felt like a 20 to 30-second earthquake.
"We certainly felt it. We've got cars out the front here and they were just rolling around in the carpark there.
"It was just rolling. The two of us here feel a bit car-sick or sea-sick still."
Archer said there were about six vehicles in the carpark and they were all seen "rocking side to side" outside when the quake hit.
"It wasn't a violent earthquake. It was just jiggling.
"We're probably kind of used to earthquakes down here, but it was just rolling for a long time. It just kept going and we're still feeling a bit yuk."
Residents of Queenstown, Wanaka, and Dunedin also all reporting feeling strong shaking.
A 4.2 magnitude aftershock struck at 10.25am - 25km west of Milford Sound at a depth of 8km.
Multiple residents in Queenstown felt the first quake and said there was a rumbling for about 15 seconds, the ODT says.
One Dunedin homeowner told the Herald she felt a short rocking motion, lasting only a few seconds, while a Wanaka resident said her windows rattled.
Clare Curran, MP for Dunedin South, was at home on the phone when the quake struck.
"The whole room shook," she said, adding that it was a rolling quake rather than a sharp jolt.
"We've got a chandelier – it's not fancy – and it was swinging back and forward," Curran told the Herald.
Her first concern was over the quake epicentre, saying that it you feel tremors in Dunedin, they're often very significant elsewhere.
Southland District deputy mayor Ebel Kremer lives in Te Ānau but didn't feel it - he was operating his digger at the time.
He'd received a flurry of text messages from many who did, who commented "oh what a beautie" and "did you feel that one?!"
Caltex Te Ānau owner Stephen Stock described the quake as "a goodie".
"We just felt the big roll come right through."
He said his priority was getting all the staff outside.
He estimated it lasted for about five to eight seconds.
Bottle-O Te Ānau staff member Vanessa Hodges felt the quake.
"The store was definitely shaking. We were shifting boxes of beer around when it hit. We just ditched the beers and ran outside."
"We are pretty used to quakes (but) this one was a lot longer and we didn't hear the rumble coming."
She said everyone was fine - and the store, including all of the alcohol, escaped any damage.
One Milford Sound resident described it as a "decent" shake and said it felt like it would have been shallow one.
He said despite being a decent shake, they were used to earthquakes. He and his colleagues were all safe and he wasn't aware of anything falling off shelves.
A spokesman for Fire and Emergency NZ southern communications centre said they hadn't yet received any calls or reports of damage in the area.
Emergency Southland manager and group controller Angus McKay told the ODT that first investigations into the earthquake indicated there were was nothing to worry about.
"Everybody felt it in Milford Sound and Te Anau. There's no damage and no injuries reported."
"It's just another reminder that we live in a shaky country," McKay said.
Several residents of the the lower North Island also felt the quake.
Scientists weren't surprised to see a large earthquake occurring in that area – in the past few years, there have been more than a dozen quakes in that range.
GeoNet seismology and strong motion specialist Dr Muriel Naguit said there had already been several aftershocks, including quakes measuring 3.4 and a 4.2, and more could be expected.
She said the quake was a result of reverse faulting. This happened when the Earth's crust was being compressed, and one block of crust moved up and over the other.
Victoria University geophysicist Professor Tim Stern said the region was New Zealand's most seismically active zone – and in 2009, saw a huge 7.8 event at Dusky Sound.
Not only did the vast and high-risk Alpine Fault extend down south to that area, but it was also a point where the Australian plate subducted beneath the Pacific plate – and Stern suspected the quake had occurred within this subduction zone.
"We have quite a complicated arrangement of very young subduction of the Australian plate going beneath the Pacific plate," Stern said.
"It happens to be orientated from west to east which is the opposite that we have under the eastern north island which goes from east to west."
After a 5.5 quake struck in the Milford area last year – sending debris rolling down South Island mountains – GNS scientists described the region as a "dog's breakfast" of tectonic systems.
By about 11am, there had been 10 aftershocks - although most weren't big enough for people to feel.
A 3.1 shake at 10.55am, 20km west of Milford Sound, was described as being weak in intensity by the 75 people who reported it on GeoNet.
More than 3700 people felt the initial earthquake, six of whom described it as extreme.