Prime Minister Jacinda Ardern is eyeing additional border restrictions following United States President Donald Trump's 30-day ban travel ban on Europe.

"I expect I'll be getting advice in the next 24 hours to move again on our border restrictions," the Prime Minister told reporters in Northland on Thursday. 

The Prime Minister's comments follow an address Trump gave on Thursday in which he announced all travel from Europe to the United States is suspended for 30 days due to the COVID-19 coronavirus outbreak.

"I will never hesitate to take any of the necessary steps to protect the health, safety and wellbeing of the American people," Trump said from the White House, adding that no nation is "more prepared or resilient" than the US.

On Wednesday, Ardern announced that all travellers from Italy will now be required to self-isolate for 14 days upon arrival in New Zealand - expanding it from just northern Italy - bringing it into line with travellers from South Korea. 

But the travel ban still only includes China and Iran, despite Australia banning travellers from Italy and South Korea to prevent the spread of the virus. 

Ardern justified not banning Italian and South Korean travellers, saying the self-isolation requirement has "had the right effect right down to the point where I imagine now we will have just citizens and permanent residents".

Ardern argued New Zealand has "some of the tightest border restrictions in the world".

Earlier on Thursday, she urged anyone who is sick not to attend work or mass gatherings as the World Health Organization declares the coronavirus COVID-19 a pandemic. 

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"If you are sick, do not go to work and if you are sick do not go to mass gatherings," Jacinda Ardern told reporters in Wellington. "That is one of the most important messages that we need to get out.

"You might not feel that unwell, but you're putting at risk others... I think there is a feeling amongst communities that if you are unwell, then going out and being at work and public places, is putting others at risk."

Despite her warning about spreading the illness, two large public events are still going forward this weekend: The March 15 Christchurch mosque attack memorial and the Pasifika Festival in Auckland. 

New Zealand has five confirmed cases of COVID-19.