As of midnight tomorrow every person arriving in New Zealand apart from those coming from the Pacific islands will have to self- isolate, Prime Minister Jacinda Ardern says.

She is addressing the media on coronavirus.

Until now, foreign travellers arriving from mainland China and Iran have been banned from entering the country. Travellers from South Korea and Italy have been asked to self-isolate for two weeks on arrival.

As of midnight Sunday every person arriving will have to isolate themselves for 14 days, Ardern says. That will mean New Zealand will have the strongest restrictions in the world, she said.

She said the measures will be reviewed in 16 days and there will be more measures and advice for self isolation next week.

All cruise ships are also being asked to not come to New Zealand until June 30. It does not apply to cargo ships.

The prime minister said it is not realistic for New Zealand to only have a handful of Covid-19 cases.

However, "New Zealand has today relative to other countries a small number of cases," Ardern said.

We have two choices as a nation, Ardern said. One is to let Covid-19 roll on, the other is to go hard on measures to stamp it out. It is in our power to slow it down, she said.

New Zealanders' public health comes first and this constitutes an unprecedented time.

"Cabinet made far reaching and unprecedented decisions today because these are unprecedented circumstances. As of midnight Sunday every person entering New Zealand, including returning New Zealand citizens and residents, will be required to enter self isolation for 14 days - everybody.

"The Pacific are exempted from this measure, they are the only ones. Anyone from this country though will be required to automatically self isolate should they exhibit any Covid-19 symptoms on arrival in New Zealand. All of these restrictions will be reviewed in 16 days' time.

"This decision will mean New Zealand will have the widest ranging and toughest border restrictions of any country in the world. We are also encouraging New Zealanders to avoid all non-essential travel overseas - this helps reduce the risk of a New Zealander bringing Covid-19 in."

In addition to restrictions on air travel, as of midnight today the government is issuing a directive to all cruise ships not to come to New Zealand until at least 30 June at which time the directive will be reviewed - this is for incoming cruise ships. It doesn't apply to cargo ships, marine or air crew, so that sea and air freight can remain open for imports and exports.

She wanted to ensure that essential airfreight such as pharmaceuticals could continue to enter the country.

"We do not take these decisions lightly, we know these travel restrictions will place a significant strain on the aviation industry and we anticipate some routes will reduce or cease for a period of time."

Photo: RNZ / Jogai Bhatt

The government will work closely with the aviation sector to support it to remain active in New Zealand so it could rebound from restrictions quickly and it would not have significant impacts on the tourism sector, exports and the economy.

There's no need for anyone, despite these restrictions, to conduct a run on the supermarket, Ardern said.

Support for businesses to be announced on Tuesday

The Finance Minister will announce an economic response including a business continuity package on Tuesday. The Health Minister will also announce further measures and public information campaign.

Advice will be released shortly on large events where people will be in close proximity to each other, events where people have travelled from overseas and non-ticketed events.

New border exit measures for those travelling to the Pacific will be put in place including no travel for people who have travelled outside of New Zealand in the past 14 days, no travel for close or casual contacts of a confirmed case, no travel for anyone who is a confirmed case and no travel for anyone who is symptomatic.

Significantly more people will enter self-isolation as a result of these measures. Health authorities have been asked to step up enforcement of self-isolation through measures such as health checks, Ardern said.

"These measures while disruptive are needed to make the space we need as a nation to prepare and manage the spread."

Read more about the Covid-19 coronavirus:

Earlier today, a sixth case of Covid-19 was confirmed by Waitematā District Health Board, and tomorrow's mosque attack national memorial service in Christchurch was cancelled due to concerns about the coronavirus.