This suggests massive restrictions could be in place for a lot longer than four weeks.

New research suggests up to 80,000 Kiwis could die from coronavirus without strict measures such as the country-wide lockdown.

It also shows that the lockdown may have to last far longer than a month to keep the strain on the healthcare system manageable.

But one of the paper's authors said New Zealand's speed at adopting a lockdown could mean we "stamp out" the disease much faster.

Auckland University Professor Shaun Hendy said New Zealand still had a chance to stamp coronavirus out.

The modelling from the University of Auckland's Te Pūnaha Matatini was provided to the Government before it made its lockdown decision, and builds on research overseas that has informed governments around the world in instituting dramatic lockdowns. On Sunday, initial modelling suggested as many as 60,000 Kiwis could die if stringent measures weren't implemented.

Assuming 20 "seed cases" and a transmission rate of 2.5 the model looks at what would happen if no attempts were made to stop the spread of the disease.

It finds roughly that within 400 days roughly 89 per cent of the population would get infected, far exceeding the capability of our hospital system to cope and causing up to 80,000 deaths.

The research models that New Zealand's hospital could deal with about 40,000 cases - so if more than 4 million people had the disease it would be vastly exceeded.

Much like the Imperial College paper which this research builds upon, the authors find that individual measures like closing schools and universities would not be sufficient to prevent large casualty rates.

Only a full mix of suppression strategies - population-wide social distancing with a lockdown and the closure of almost all businesses and schools - could keep the case numbers down enough for the healthcare system to cope, with a mortality rate of just 0.0004 per cent: About 20 people.

However the cases would spike the moment these measures were lifted, unless a vaccine had been developed in the meantime.

This suggests massive restrictions could be in place for a lot longer than four weeks.

However the full lockdown might not need to be maintained - or even be desirable.

Like the Imperial College paper the research looks at a "mitigation strategy" where the Government reduces restrictions when the infection rate is low and then rapidly clamps them back on when the healthcare system approaches capacity. This would be useful to gradually develop "herd immunity" for the disease while never allowing it to exceed the capacity of hospitals.

This could involve cycling between level 4 and 3, possibly with different regions of the country being in different levels at the same time, as the prime minister suggested on Monday.

"In general mitigation requires an initial period of weak control to allow the epidemic to establish, then an extended period (3-4 months) of very strong control. This can be followed by periods when control measures can be loosened, but strong control needs to be re-established when cases increase towards hospital capacity," the researchers write.

But they caution that this kind of huge social control over daily life has yet to be fully tested in a comparable country, with only South Korea and China managing to get an transmission rate below 1.

"In those countries, this has been achieved by extremely intensive measures, including mandatory and strictly enforced quarantine, huge amounts of resources devoted to contact tracing, electronic surveillance of citizens' movements, etc.

"It remains unknown whether this will be achievable in practice in New Zealand. There is no evidence that it has yet been achieved in comparable, western democracies, including those that have instigated major lockdowns such as Italy."

They also note that this process could take up to two and a half years to build up this herd immunity.

POSSIBLE TO 'STAMP IT OUT' EARLY

One of the paper's authors Shaun Hendy told Stuff it was possible that New Zealand's actions could see the disease stamped out relatively quickly.

He noted that the paper was written before the Government announced the lockdown and it didn't take into account aggressive contact tracing and testing.

"The fact that we've gone early and we've gone for that suppression strategy means we have brought some time for for those contact tracers and testers to stamp it out," Hendy said.

"We are possibly unique amongst our normal comparative countries."

Hendy said New Zealand had a "bit of luck" as the disease had reached our shores relatively late and there was still not a huge amount of confirmed community transmission.

He said it was key that people obeyed the lockdown instructions - particularly in large urban areas with a concentrated population.

Like the Government he expected the total number of cases to continue to rise as more people came to New Zealand from overseas over the next week and a half, before hopefully dropping off.

Prime Minister Jacinda Ardern said on Thursday that much of the modelling the Government was basing its decisions on was already in the public domain.

She has not yet given a timeframe to release the full Cabinet paper which sets out the unprecedented decision to shut down most of New Zealand's economy.

When announcing the move on Monday she said she had seen research that showed tens of thousands of New Zealanders could die without strict controls, and this was enough to sway her.

Director General of Health Ashley Bloomfield has said it was possible cases could peak in 10 to 12 days and begin to fall from there.