A public health professor says the lockdown period is critical for people to change their behaviour and not share the Covid-19 virus.
Professor Michael Baker from Otago University and other health professionals urged the government to implement the level 4 lockdown to break the chain of transmission. It began at 11.59pm on Wednesday.
He told Morning Report the move was further allowing the country to build capacity to stamp out the virus, putting it on a "path of elimination", similar to the one taken by China.
"I know I had my best night's sleep on Wednesday. I was imagining all those unseen chains of transmission around New Zealand that we might have missed gradually getting snuffed out because people are no longer sharing the virus around," he said.
"It's so critical in this period that people change their behaviour and not share this virus."
Recent modelling predicted the lockdown could save about 80,000 lives across New Zealand. Dr Baker said large-scale testing, contact-tracing ability, and tighter border control systems were needed to contain the illness.
It would also mean health authorities would have a better handle on numbers infected in the community and would allow the government to better determine when the lockdown could end.
"There were 2400 tests done a couple of days ago and that is really good news for New Zealand," he said.
"Community-based assessment centres are ramping up and they'll be able to see more and more people. Their testing capacity is ramping up. The other part, which is something we haven't had in the past, is having very large teams who can do contact tracing.
"It's going to have to be set and ready to go on a very large scale if we need it, because all the modelling shows that you have to detect the cases and isolate them, but after that you have a very short window of opportunity to follow up all of their contacts and quarantine them."
He said strict border controls would be essential when the country came out of shutdown.
"The other thing that is happening is tightening border controls and quarantine and that's critical now, but it will become even more critical as we come out of the shutdown period, that anyone coming into New Zealand does go into quiet tightly-managed quarantine situations."
His comments came as China closed its borders to foreign nationals to avoid reinfection, after having successfully contained the spread of Covid-19 within the country and especially around Wuhan City, the epicentre of the virus' global spread.
Baker said New Zealand doesn't have a pandemic, as it so far has had a trickle of cases.
Baker said he wasn't worried about the virus mutating further as it spread across the globe.
"These viruses are under huge selective pressure and generally the selection is towards variance that is more infectious and less lethal.
"So what we might tend to see over time is the virus will become part of our normal bugs that infect our respiratory tract like the other four coronaviruses."