There are no new confirmed or suspected cases of coronavirus in New Zealand, Director-General of Health Ashley Bloomfield says.

It's the fourth day in a row that no new cases have been announced.

All five confirmed cases are now being cared for at home. That includes the first patient diagnosed, who was discharged from Auckland City Hospital yesterday.

All close contacts of the confirmed cases had been contacted by public health staff, Bloomfield said.

"It's very unusual for us to get every single casual contact - you can imagine if it was a mass gathering like a concert," he told reporters.

"However what the evidence suggests is that to be successful in containment you need to get at least 80 per cent of those casual contacts, and we have been able to do that in all of the cases, both confirmed and probable."

A "close contact" is defined as being within one metre of a person for more than 15 minutes.

One of two probable cases - a woman in her 70s who had been on the Grand Princess cruise ship - who had been treated at North Shore Hospital was also now home.

"Of the other confirmed cases, none is requiring hospital care at this point."

Bloomfield stressed that it was up to every New Zealander to prevent an outbreak.

Everyone - including himself - was guilty at times of going to work with a runny nose and a sore throat, or sending their slightly sick kid to school. Now was the time to be much stricter, he said.

"Please stay home if you are unwell".

This was particularly important with large public events such as Auckland's Pasifika festival and the memorial service for the Christchurch terror attacks this weekend.

Healthline had fielded 2930 calls yesterday - double the number it had taken on the same day last year.

There were now 9039 people or households that had registered for self-isolation since the process began - 2145 of them remain in self-isolation.

Bloomfield thanked everyone who had taken the step to self-isolate, saying it was one of the most important tools for addressing Covid-19.

He said there had now been 331 negative tests for coronavirus - 28 tests were being done today around the country.

A possible case of coronavirus in Northland has been tested and come back negative. A Northland person who was at the Tool concert and was unwell and in isolation has also been tested - those results would be back today.

All tests were being carried out in New Zealand now using the same testing process as is used around the world, Bloomfield said. He was confident that the tests coming back as negative here were correct.

Bloomfield said the ban on travel from China and Iran was being looked at daily and reviewed by Cabinet ministers each week.

Travellers from northern Italy and South Korea are required to self-isolate for 14 days; ministers will consider later today whether to add more areas to that restriction category based on advice received yesterday from the technical advisory group.

This week the ministry has been looking at specific places that could encourage the spread of Covid-19. One of those is aged residential care.

Bloomfield has asked for a message to go out to all aged care facilities asking sick people not to visit until they have been well for at least 48 hours.

Visitors should also be asked to practise "effective social distancing" - previously described as staying around 2m away from other people.

New Zealand will be dealing with Covid-19 for at least a few months, he said.

Slowing its spread in order to "flatten the curve" was crucial to limit its impact on New Zealand's health system.

Normally New Zealand's pandemic plan would suggest actions like closing schools and cancelling mass gatherings only if the pandemic had progressed further - to the "manage it" phase, Bloomfield said.

But because of the nature of Covid-19, it was important to have those tools read to be deployed now, if necessary, in order to slow the virus' spread.

In response to reports that McDonald's NZ has temporarily banned reusable "keep cups" due to the risk of spreading the virus, Bloomfield said people should not be heading out to McDonalds if they were symptomatic anyway.

"If you've got your keep cup and you're going out for a coffee we'll assume you're well."

Yesterday Bloomfield said protecting the health of New Zealanders is their number one priority.

"It's good the key public health measures of strict border controls, self-isolation for people who have come from overseas hot-spots or been in contact with local cases have had the desired impact so far.

"Now is the time to be even more vigilant," Bloomfield said.

"Everyone can help by ensuring good health etiquette – washing hands for twenty seconds, sneezing into your arm and not touching your face," Bloomfield said.

"Fundamental to this is not putting yourself or others at risk if you are unwell - not going to work or being out in public if you are sick.

"All of us have a role to play in stopping further spread."

More than 115,800 people have been infected worldwide and over 4000 have died.

The situation has become increasingly dire in Italy which now has a country-wide lockdown as it now has more cases than China with 10,149 infections and 631 deaths.