Modelling work the health ministry is commissioning from experts is expected to predict up to half of New Zealand's population could contract coronavirus.

A spokesperson for the ministry told Stuff on Wednesday it was working with public health experts to develop modelling scenarios for the virus. It is understood the work has been under way for some time.

"This information will provide us with a reasonable worst-case scenario which will guide our planning," the spokesperson said.

On Wednesday, director-general of health Dr Ashley Bloomfield told media that mass gatherings and school closings could be employed to contain the spread of the virus here. New Zealand has a total of five confirmed cases, and two probable cases.

LUIS ASCUI/GETTY A man wearing a mask waits in a line to be screened for coronavirus outside the Royal Melbourne Hospital.

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Professor Michael Baker, from the University of Otago's public health department, is one of the experts helping the ministry with the work.

He and others had been "bouncing ideas" around for quite a while, to help with the ministry's planning process around the virus moving forward.

However, he said a point had not yet been reached where the work was ready to be released.

Baker was unable to confirm what the modelling estimates showed currently, however reiterated any modelling work was just that - "a scenario" - not reality.

SUPPLIED Professor Michael Baker from the University of Otago says it is important to remember any modelling is just "a scenario", not the reality of right now.

Internationally, epidemiologists had predicted that countries could see infection rates of between 40 and 60 per cent of their total populations if the virus was not controlled, Baker said.

Dr Samantha Murton earlier this week told Newshub that estimates showed up to 50 per cent of New Zealand's population could contract the virus.

Baker said New Zealand's health ministry was trying its best to contain the spread. News of no new reported cases over the past four days indicated the country may be succeeding in that respect.

Several countries were exemplary in controlling the spread of the virus, including Singapore, Taiwan and Hong Kong, he said.

Italy's PM orders 60 million Italians to stay at home to fight the coronavirus. Queues have formed at supermarkets and people need documents to travel.

Cases in mainland China also appeared to be levelling out, however it had imposed "quite strong measures" to achieve that.

New Zealand should be using "each one of these precious days" for maximum containment efforts, he said. That work included case isolation, contact tracing and quarantine of contacts.

The country was at a critical stage for containment of the virus, he said.

When Prime Minister Jacinda Ardern was asked about transmission rates on Wednesday, she said that it would come down to how well public health messages were followed.

MARK TANTRUM/GETTY Prime Minister Jacinda Ardern says the transmission rate will come down to how well public health messages are followed.

People who felt unwell should stay at home, wash their hands, and make sure to cough and sneeze into their elbows, Ardern said.

"They might sound like trivial messages but actually for those countries that have managed to smooth and slow the path of transmission, those are the kinds of practices that are making all the difference."

Meanwhile, the Government announced new self-isolation rules for those travelling back to New Zealand from Italy on Wednesday.

As at Wednesday, there have been more than 119,000 cases worldwide, and more than 4200 deaths.