SYDNEY - As New Zealand's Covid-19 numbers were slowly rising like the rest of the world on March 23, Prime Minister Jacinda Ardern decided that instead of gradually preparing for a serious outbreak, the country should try to completely eliminate the virus.

At that stage, NZ had experienced no coronavirus-related deaths but as Ms Ardern famously declared: "We currently have 102 cases. But so did Italy once."

So she introduced a four-week, strictly-enforced lockdown that started 48 hours later. All schools and non-essential businesses have been closed since March 26. The country's five million residents have been ordered to stay at home, except for brief exercise, shopping and medical visits. Police and the military have been deployed to enforce the measures.

And it appears to be working.

Singapore PM Lee Hsien Loong spoke to Ms Ardern last week, later noting that NZ's numbers only started to come down on Day 11 of its approach and that Singapore, which was also adopting a strict response, will hopefully also "see positive results" by that point.

"We are both implementing strict circuit breaking measures, to break transmission of the virus and squeeze the cases down," Mr Lee said in a Facebook post.

"If we all comply strictly, as the New Zealanders have done, hopefully by our day 11 we too will see positive results."

In NZ, on the 11th day after introducing the lockdown, the daily increase of cases peaked at 89. The next day, they dropped to 67 and have since gradually declined. There were 17 new cases on Tuesday (April 14) , bringing the total number of confirmed and probable cases to 1,366. Nine people have died.

Ms Ardern said on Tuesday that NZ was past its peak but must not yet relax its measures. "We are successfully over the peak but that is not the same thing as being out of the woods," she said.

Professor Michael Baker, a public health expert who helped devise NZ's strategy, said most Western countries had adopted an approach typically used to combat influenza outbreaks which involves "flattening the curve", or trying to reduce the peaks. Instead, he said, he and his colleagues realised that NZ - an island nation which was not yet overwhelmed - could actually try to completely eliminate the virus.

"We felt actually this was more like a Sars virus and that basically containment with the goal of elimination was actually viable," he told ABC News this week.

Prof Baker said Covid-19 had a longer incubation than influenza - about five or six days compared with one to three days - which meant that isolating known cases and tracing their contacts was likely to be more effective.

"It meant that those containment measures of stamping it out, so that's case identification, isolation, contact tracing, quarantine, they can work if they are done very rigorously," he noted.

NZ's measures are due to end on April 22 but there is disagreement about exactly how it should emerge from its lockdown.

On Monday, the government will decide whether to move out of its lockdown next Thursday. Its restrictions would then be eased by one level to Level 3. This would likely mean mass gatherings remain banned and public venues such as cinemas and libraries stay closed but some businesses and schools and universities could potentially reopen.

However, a group of academics this week said the country should more quickly get out of its lockdown and go directly to Level 2, allowing most schools, businesses and universities to reopen. Leisure and domestic travel would be allowed but vulnerable people would still self-isolate.

One of the group, Dr Simon Thornley, a public health expert from Auckland University, said the risks from Covid-19 were not as bad as feared. The real threat, he said, was from putting excessive pressure on the health system.

"This is not the disaster we feared and prepared for," he said. "Elimination of this virus is likely not achievable and is not necessary."

But one of the architects of the elimination strategy, Professor Nick Wilson from Otago University, disagreed, warning that moving out of the lockdown too soon or too fast could risk mass fatalities.

"If we do eliminate it quickly, we can open up the economy much earlier than other countries and use border controls as a means of keeping it out," he told the Stuff website on Tuesday.

"As an island nation, we have much better options if we keep that quarantine until we have a vaccine."