GNS scientist Kate Clark has outlined what would happened if a large "megathrust" earthquake struck on the Hikurangi subduction fault east of New Zealand.
The fault runs the length of the east coast of the North Island, across Cook Strait and down to Kaikoura, and is the area where the Pacific tectonic plate pushes underneath the Australian plate.
Speaking this morning to TVNZ 1's Breakfast programme, Dr Clark said a magnitude nine earthquake on the fault, which is the worst-case scenario, would be felt across the country with a very long period of shaking.
Following the quake, a tsunami would likely be triggered, giving people on the coast just seven minutes, in some places, to escape from a wall of water.
"It would probably generate very widespread ground shaking and a very long duration probably felt over most of New Zealand," Dr Clark said.
"Possibly the deadliest impact would be the tsunami that it triggers - it would inundate low-lying parts of the east coast very quickly - within seven to 30 minutes we could get tsunami inundation."
It's difficult to predict where and when an earthquake will take place, but Ms Clark said further study is being undertaken along the faultline to understand how common large earthquakes have been.
"We see evidence for these earthquakes along the whole Hikurangi margin," she said.
It will open to the public from December 15 but today locals were given the first tour.
"Our understanding of the geological record is not really complete enough to forecast the size and the timing of the next earthquake, but there's a lot of research going on at the moment."
The most important thing, she said, was "having your emergency kit ready, knowing your tsunami evacuation route, having a family emergency plan and following the advice that we get from emergency management".
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