Prime Minister Jacinda Ardern gave some more details about the government's decision to require all international travellers to self-isolate for 14 days on arrival.

The deadline for travellers to arrive in New Zealand before they must self-isolate for 14 days has been moved to 1am Monday.

The original deadline, announced by Prime Minister Jacinda Ardern, was midnight Sunday.

Board of Airline Representatives NZ executive director Justin Tighe-Umbers said on Sunday the change had been made to reflect the reality of Sunday night flight patterns, when flights typically landed late in the evening.

The deadline referred to the time a plane touched down on the runway and passengers could come through border controls after 1am without needing to self-isolate, he said.

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Meanwhile, Ardern said quarantine powers may be used to keep possible Covid-19 coronavirus cases in hospital if they refuse to self-isolate.

Ardern, in an interview on Q+A on Sunday morning, explained in greater detail how the Government's decision to require all international travellers to self-isolate for 14 days was expected to work.

There would be more "spot checks" on those in self-isolation. People would be asked to take private transport from the airport, and domestic flights would still be taken by people who have returned.

Ardern also said an economic stimulus package would be "the most significant package that I will announce while I am prime minister", signalling it will be more important than the $12 billion infrastructure announcement in January.

On Saturday, Ardern announced that everyone arriving in New Zealand would have to self-isolate themselves for 14 days, beginning midnight on Sunday.

Ardern on Sunday said that, while 10,000 people had self-isolated successfully without needing strict enforcement, public health officials and police could use quarantine powers to compel people to self-isolate.

"We can put you in a facility and monitor your movements".

These facilities include a medical facility or hospital, and officials could be stationed at doors to stop those quarantined from leaving.

When people entered the country, they would be asked to complete a border entry form and would have to speak with a nurse who would explain the self-isolating requirements.

People would be asked to take private transport from the airport to their home. Those travelling on domestic flights were advised to reduce close contact with people and maintain social distancing, Ardern said.

They would then receive calls from Healthline to ensure they were self-isolating. "Spot checks" by public health officials would be increased, Ardern said.

She also explained that self-isolation didn't mean you couldn't go outside. Self-isolation was more about reducing contact with others and staying confined to your home.

"You can take a walk around the block, but you can't go into public places and places where you're interacting with others".

Ardern said she did not have figures on how many people may have to self-isolate. The number of travellers had dropped away.

She said she had been advised that, for people who caught the virus, 80 per cent would be okay and 7 per cent would be "more acute".

There will be more Covid-19 cases in New Zealand, she said.