The Prime Minister urged Kiwis to remain cautious, but also reflected on some positive insights from Dr John McDermott, who leads the data science team at the Asian macro-economic advisory firm, Wigram Capital Advisors.

Dr McDermott's modelling - which Ardern cited during her press conference on Sunday - has suggested the country might have had 4000 cases of COVID-19 by now, were the country not in lockdown.

Dr McDermott has said if the number of new cases reported are under 60, it could be the start of the curve flattening, which could ultimately lead the Government to consider relaxing some of the rules after the four-week lockdown is complete.

Ardern referenced Dr McDermott's suggestion that "when the numbers start to fall, that is the first indication your interventions are working".

He says every country will go through three phases of COVID-19, starting with an outbreak of the virus, followed by a levelling of new cases, and then finally light at the end of the tunnel when the number of new cases starts to drop.

"He is cautiously optimistic that what we're doing with the lockdown is making a difference, but as with any data analysis, there are always possibilities of setbacks," Ardern said.

"But, for the moment, we do appear at this early stage to be on track."

The Prime Minister said the success New Zealand has seen so far underlines the importance of sticking to the self-isolation rules, and that now is "not the time to change any behaviours".

It follows positive feedback from Otago University Professor Michael Baker who told The AM Show last week New Zealand is looking like the only Western country with a chance of eradicating COVID-19.

The Ministry of Health has reported no additional deaths, meaning New Zealand has had just one COVID-19-related death compared to more than 10,000 in the United States and more than 74,000 worldwide.

There are currently 12 people in hospital in New Zealand because of COVID-19, with one in a critical condition, but more than 240 people have now recovered from it.

So far, 42,826 tests have been carried out across the country.