Prime Minister Jacinda Ardern says New Zealand will have more coronavirus cases as she defends the Government's stringent travel restrictions.

Any person from any country, excluding the Pacific islands, is now required to self-isolate for 14 days upon arrival to the country, and Ardern has encouraged all New Zealanders to avoid all non-essential travel overseas.

As well as affecting thousands of peoples' travel plans, the move is expected to significantly impact Kiwis' jobs and New Zealand economy.

Ardern told TVNZ's Q+A this morning: "We will have more cases in New Zealand. We will."

The Government's goal was to avoid a large-scale community spread of the virus.

"What we're trying to do is slow the speed with which we have them."

Eighty per cent of people will have mild to moderate symptoms, and they'll stay at home and should be fine. Hospital space needed to be saved for more severe cases.

"At the upper end, 7 per cent roughly might be much more acute," Ardern said.

Public health were responsible for enforcing the new travel restrictions, but police were also able to help.

Questions for every passenger heading from New Zealand to the Pacific would help to keep that region safe, Ardern said.

The Government has been constantly looking at global developments, and the new restrictions unveiled on Saturday were the nest step to "go hard" to flatten the curve.

The restrictions were about putting health first, and to keep the pressure off the public health system as the number of positive cases is expected to rise.

She said self-isolation didn't mean you can't go outside, but you shouldn't go to public places. It "pretty much" meant you should stay at home.

That was because the virus spread via droplets, so if you are close enough to someone as they coughed, you could get infected.

Self-isolation had been successful and people had been compliant. People arriving at the airport were registered, and spot checks would be stepped up to ensure compliance.

Ardern said authorities had the power to quarantine people at a medical facility if they were not self-isolating, but that power had not been used so far.

The restrictions on Italy so far had seen travellers from that country reduced to a trickle, she said.

The same restrictions that have been on South Korea saw flights from that country essentially stop, she said.

Ardern said the 10,500 New Zealanders who have self-isolated were so worried they might infect someone that many had stayed at home for longer than 14 days.

Advice to international travellers arriving in NZ

She said testing people at the border wouldn't be effective. Some tests could produce a false negative result, which would lead to complacency.

Those arriving at the airport should get private transport back home, rather than taxis.

Some people arriving back into New Zealand who need to take a domestic flight to get home will need to be cautious and keep their distance as much as possible, Ardern said.

By next week, 1500 people a day could get tested, and it was up to clinicians who needed to be tested, Ardern said.

At the moment, transmission and close contacts can be traced, but community transmission will make contact tracing will be harder.

She said the economic package will be before Cabinet tomorrow and they will be announced on Tuesday.

"This will be the most significant package that I will announce while I am Prime Minister."

Covid-19 has now infected more than 145,000 people around the world and six in New Zealand - and that is expected to rise.

More than 10,000 people have self-isolated in New Zealand, with the number expected to dramatically increase.

The new travel restrictions, which Ardern described on Saturday as the toughest border restrictions in the world, will be reviewed after 16 days.

People who have travelled outside of New Zealand in the past 14 days are also not permitted to travel to the Pacific islands, while cruise ships will be banned from entering New Zealand until the end of June.

Cargo ships and essential air freight will still be allowed to enter the country for things like pharmaceuticals.

Other restrictions — such as denying travel for anyone who shows symptoms — have been introduced.

The Government is also preparing to release a directive on public events this week. It is expected to follow the lead of other countries, which have banned gatherings of more than 500 or 1000 people.

Ardern encouraged Kiwis to "Enjoy your own backyard for a time".

Cabinet will tomorrow discuss the details of how to help businesses and the economy stay afloat.

Bagrie Economics chief economist Cameron Bagrie said the economic response needed to be significant because the new travel restrictions will create "economic carnage".

"A recession is inevitable, the question now is how bad?"

ANZ's chief economist Sharon Zollner said the Government's move was a "body blow to tourism to lessen the odds of a king hit to New Zealand's economy and people".

"Mitigating the human toll of this virus will come at a high economic price," she said.

"But that's unavoidable, and we can see from the experiences of other countries that the later that leaders act boldly, the greater the cost will be."

Finance Minister Grant Robertson will on Tuesday announce further details of the response, as well as the Government's wider "economic response".

Employment New Zealand has issued guidelines for the workplace which state that employers should not require or knowingly allow workers to come to a workplace when they are sick with Covid-19 or if they have been advised to self-isolate under public health guidelines.

If they do, they are likely to be in breach of their duties under the Health and Safety at Work Act.

And if a worker comes to the workplace after being told not to, they can be suspended from work.