No amount of planning could prepare the country for the reality of a large-scale earthquake, disaster officials have warned.
The South Island Alpine Fault Earthquake Response Forum was in Nelson this week as part of its awareness-raising road-show. The region was vulnerable to large quakes in both the South Island and the North Island, which was at risk from the Hikurangi subduction zone.
The Alpine Fault, which runs almost the length of the South Island, has ruptured about every 300 years for the last 24,000 years.
The last time was in 1717.
Scientist Caroline Orchiston, who was leading the response planning for a possible Magnitude 8 quake on the Alpine Fault, said Nelson and Tasman might experience the equivalent of a magnitude 6 or 7 quake, with shaking lasting up to two minutes.
But the effects will be felt far and wide.
"There will be widespread damage to our lifelines infrastructure, in other words our roads, our electricity and water supplies, so it's not just about what's happening in your region.
"In an Alpine Fault case it's across the whole South Island, and in fact the lower North Island might feel the indirect impacts as well," Dr Orchiston said.
The head of Marlborough's Emergency Management group, Brian Paton - who left his badly damaged Blenheim home to help steer the emergency response to the 2016 Kaikōura earthquake - said as bad as that was it was only a rehearsal for what could happen when the Alpine Fault ruptured.
He said despite efforts to bolster response efforts, the region was still not ready for the "Big One".
"No, we're not really. An event like this would be so enormous that you could be as prepared as possible ... but when you have 30,000 people that need somewhere to stay, and one solution is to buy enough accommodation to put those people in, but that's not the reality."
The government's temporary accommodation service provider was part of the AF8 (Alpine Fault Magnitude 8) response planning.
Engagement adviser Mike Heyward said the modelling showed up to 20,000 homes in the South Island could be damaged or destroyed in an Alpine Fault quake.
He said there was no money to buy spare homes in readiness for an emergency of this nature, as the priority now was social housing needs.
He said temporary accommodation in the aftermath of an emergency was likely to be basic.
"Tents and campervans are realistically an option because they're easy to get to places.
"We're trying to find all sorts of options and there are more out there - we've got to look at what other countries are doing and be better prepared for this."
Mr Heyward said local authorities could help by ensuring their district plans were flexible enough to cope with sudden change.
He said right now, the rules impeded emergency solutions such as being able to build a temporary second home on a single site.
"So we're asking councils to consider that when there's an emergency, could you do things differently to accommodate a short-term, temporary accommodation solution."
Knowing what to do
Brian Paton said what had improved since the Kaikōura quake was knowing what to do immediately.
He said they now had an action plan that covered the first hour of a large-scale emergency response.
"And there in black and white it will tell me the basics, or certainly the bullet points of what I need to do ... we've got a safety plan sorted out, we've got how we're going to talk to one another, who's going to do what in the first hour's shift."
A key message from Civil Defence was that help might take days to arrive, and people need to be prepared with enough emergency food, water and basic essentials including medical supplies to last several days, and to have an evacuation plan.
Emergency planners were now gearing up for a national AF8 exercise in September next year.