Kiwis who return to New Zealand could find themselves quarantined in hotels, Prime Minister Jacinda Ardern says.

The Government is looking into quarantining Kiwis returning from overseas.

Prime Minister Jacinda Ardern said tightening up the rules was her current focus.

On Monday, Ardern announced the country would be going into lockdown for about four weeks.

RNZ There are a lot of questions from New Zealanders as the government plans for the country to go into level four Covid-19 alert - full lockdown. Checkpoint's Nita Blake-Persen has been looking at the official government websites and provides some answers.

New Zealand's alert level has been lifted to three and would move to alert level four at 11.59pm on Wednesday.

Ardern planned to making an announcement on quarantine measures in the coming days.

KEVIN STENT/STUFF Prime Minister Jacinda Ardern said wants to further tighten the rules around returning travellers.

They continued to be a risk in New Zealand but they had to be allowed to return home, she said.

"But we also have to manage this risk. I have asked our team to expedite the work on managing that risk in a way that will be seen as much harsher than currently because that is what is required."

She confirmed the Government was working through options that could see people sent on buses to hotels.

The option would be based on the scale of the ongoing return of Kiwis, she said.

"We are working hard to try and anticipate the numbers that we will be dealing with and build around that. It is not a small task."

It was only now when returnee numbers were smaller that something could potentially be done, she said.

"The majority of our cases have been New Zealanders who have had overseas travel. Having every single one of those quarantined at the border would simply not have been possible," Ardern said.

"Now that our numbers are smaller, we are looking at alternative ways to add that extra guarantee. I want further tightening up around returning travellers," she told Morning Report on RNZ.

However, New Zealanders stranded overseas are now being urged to stay where they are as Ardern warned some Kiwis will be trapped.

The Government had still maintained and supported Air New Zealand to guarantee certain routes but that required them being able to transit through countries and some traditional routes through Asia had ended, she said.

"It is becoming harder if not impossible in some areas."

"If we have no ability to transit through a country on the way back to New Zealand then it becomes very difficult to bring people home."

Going forward, there would be people who wont' get home - even with the Government's best efforts, she said.

Last week Foreign Affairs Minister Winston Peters said more than 80,000 Kiwis could be left stranded if they didn't come home now.

He urged New Zealanders overseas to return home immediately as commercial flights began to dry up, but some were struggling to follow that advice as they were caught in lockdown overseas or were already unable to find flights.

The All of Government Covid-19 National Response team gave an update on Monday following Ardern's lockdown announcement.

All of Government Controller John Ombler said the influx of people into the country had significantly reduced and that health officials would continue to screen arrivals.

As people arrived they would be required to go into self-isolation, he said.

Those who lived close by could go directly home but if they lived a distance from a point of landing, other self-isolation arrangements would be necessary.

The Defence Force and Air New Zealand were standing by to undertake mercy flights - to do what they could with requests to help New Zealanders, he said.

Earlier this week Director-General of Health Dr Ashley Bloomfield mooted that a quarantine measure could be put in place.

In February, Whangaparaoa military training base in north Auckland was turned into a quarantine centre for New Zealanders returning from Wuhan, the epicentre of the novel coronavirus outbreak in China.

When Stuff asked about the quarantine possibility on Friday, Immigration Minister Iain Lees-Galloway said he could not comment and referred Stuff to Health Minister David Clark.

Clark has been asked for comment.