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The prime minister said today 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," says Jacinda.

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 - in effect as of midnight Sunday - 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 for cargo ships.

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.

We have two choices as a nation, says Jacinda. 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 consitutes 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 likely, 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."

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

Read more about the Covid-19 coronavirus:

• Covid-19: What you need to know
• Self isolation - your questions answered
• Touching your Face: Why do we do it and how to stop
• Scientific hand-washing advice to avoid infection
• More Covid-19 news

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.