A mandatory quarantine at the border will be imposed to stop coronavirus spreading from new arrivals.

The Government is also stepping up contact tracing and is in talks with the Singaporean Government about using its Bluetooth-based app.

The strict two-week quarantine of all Kiwis returning to New Zealand will take effect from 11.59pm on Thursday and will see Kiwis housed in 18 hotels while quarantined.

Liu Chen/RNZ The strict two-week quarantine of all Kiwis returning to New Zealand will start at 11.59 on Thursday and will see Kiwis housed in hotels.

Prime Minister Jacinda Ardern announced the measures at her daily briefing on Thursday.

She signalled the move earlier this week and said the Government was considering advice but the Government has come under pressure for not moving faster on the issue.

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It's understood that sorting out hotel capacity was one of the reasons for the delay.

A network of up to 18 Auckland hotels would be used to implement this approach, of which one to two would be specifically set aside for those under strict quarantine conditions.

She did not rule out using the defence force to enforce the quarantine.

MARTIN DE RUYTER/STUFF Police at Nelson Airport to meet a special Air New Zealand flight from Auckland carrying passengers who had recently arrived in New Zealand from overseas, and had been in self-isolation in Auckland hotels.

WATERTIGHT BORDER

No matter what level New Zealand was at in the future, the border needed to be tightly managed, she said.

"That's why from midnight tonight every New Zealander boarding a flight to return home will be required to undergo quarantine or managed isolation in an approved facility for a minimum of 14 days."

The requirement for 14 days of quarantine or managed self-isolation in a government-approved facility, would be a prerequisite for anyone entering the country in order to keep the virus out.

As an island nation New Zealand had a distinct advantage in its ability to eliminate the virus, but the borders were the biggest risk, she said.

The Government had gone harder earlier with border measures compared to other countries, she said.

But even one person slipping through the cracks and bringing the virus in could see an explosion in cases as was observed with some of the big clusters.

HOW MANAGED QUARANTINE WILL WORK

New Zealand's borders have already been shut to all non-residents, except for a few narrow exceptions.

Those arriving at this point have been quarantined if they displayed symptoms or did not have a suitable plan for "self-isolating" at home.

What is different is that everybody who now arrives at the border will either be put into quarantine or into assisted self-isolation in hotels.

Everyone would be kept distant from others in the facility.

"To be absolutely clear, no one goes home. Everyone goes into a managed facility," she said.

Those who are symptomatic or being tested for Covid-19 will be put into quarantine and not allowed to leave the room.

Someone in assisted self-isolation would only be allowed to leave the room for a walk or fresh air.

In order to get the measure up and running immediately, the Government would initially pay for the rooms, food and all other needs such as essential services, Ardern said.

Border control was likely to be part of the system for some time to come, so the Government had not ruled out using co-payments in the future, she said.

When asked how much the managed quarantine would cost the Government, she said contract negotiations were underway but would seek the best value for New Zealanders.

"As you would expect, we are seeking to make sure that we maximise savings for the taxpayer at a time when demand for hotels is very low."

The quarantining of returning New Zealanders will be a mammoth undertaking, she said.

MARK MITCHELL/POOL Prime Minister Jacinda Ardern has announced mandatory quarantining at the border for Kiwis returning home.

GETTING HOME TO REGIONS

The Government recognised the need for people to connect to their homes around the country after the 14 day period, she said.

It will classify relocation after an international flight as qualifying for essential access to domestic airlines.

WHY NOW?

About 40,000 New Zealanders had returned home since March 20, when the border was closed to foreign nationals.

"That is more than all of the hotel rooms across the country that we could have properly housed people in."

There had always been urgency around the matter but it could not have been done from the beginning, she said.

Now there was a major reduction in New Zealanders returning.

Since the beginning of Level 4 about 6500 have returned, reducing to 40 on Wednesday.

National leader Simon Bridges said the decision was a good one - and one his party had been pushing for.

"I'm really proud of National and the tens of thousands of New Zealanders who have spoken up on this," he said.

COVID-19 CASES: 1239

The quarantine move comes as Director-General of Health Dr Ashley Bloomfield announced 29 new cases of coronavirus. Six of these were probable and 23 were confirmed.

This brings New Zealand's Covid-19 cases total to 1239.

While 317 people have recovered, there are 14 people in the hospital and four are in intensive care.

There were still 12 significant clusters, with Marist, Bluff and Matamata remaining the largest.

THE PLAN IS WORKING

Thursday was day 15 of the Alert Level 4 lockdown and the halfway mark, Ardern said at her daily briefing.

Modelling provided to her office by economist Rodney Jones on the eve of the lockdown suggested New Zealand was on a similar trajectory to Italy and Spain and that our 205 cases on March 25 could have grown to over 10,000 by now without the actions we have taken together.

And new modelling due to be released later on Thursday by Te Punaha Matatini suggested that the current controls at Alert Level 4 have already had a significant impact on new case numbers and we are on track to meet their most optimistic scenario.

"Instead of the horrific scenes we have seen abroad we are at 1239 cases, and the total number of cases has fallen for the last four days with 29 new cases today, the lowest daily number of cases since the 23rd of March, before the lockdown began.

"We are turning a corner, and your commitment means our plan is working," Ardern said of the public's effort.

TRACING APP

Singapore was planning to open source its technology and the Government has made initial contact with the Singaporean Government to register interest in using the Bluetooth-based app, she said.

TraceTogether can record interactions between a phone and any other phones nearby that have the app installed.

The data is stored on the phone and if the user tests positive they then release the data to the Government for contact tracing. Close contacts can then be automatically notified of their need to self-isolate and be tested.

"I will have a phone call with Prime Minister Lee of Singapore this evening where I will be discussing this technology further," Ardern said.

Meanwhile, the Ministry of Health was working on a locally developed app that would assist with contact tracing, she said.

It was currently in the early stages of development and would have basic functionality, but even that would help update our national health database with user contact details, she said.

While apps were useful she believed they did not solve everything.

TESTING

The Government wanted to do even better with testing, she said.

"We will be maintaining high levels of testing and supplementing it with additional testing to ensure we have greater levels of certainty around the decline in the viruses spread."

With the three pillars of border controls, rigorous testing and contact tracing, New Zealand had what it needed to win the Covid-19 marathon, she said.

"But I know in a race it's important to have some signposts. To know where we are, and exactly what we need to do when we get there so we can all plan."

TIMELINES FOR KEY DECISIONS

Level 4 had come with some heavy restrictions, which had required difficult decisions around services and businesses that could and could not operate, she said.

But she stressed, leaving it early would not happen because that would see the country go backwards.

Next week the Government would give similar more detailed guidance on what life at Level 3 would look like.

"It is then my intention that on the 20th of April, two days before the lockdown is due to finish, Cabinet will make a decision on our next steps. That's because we need to use the most up to date data that we have to make that decision."

That meant, if the country was ready to move to Alert Level 3, business would have two days to implement arrangements.

"In the meantime I ask every business to use the time you have to prepare for what every alert level may mean for you. Treat COVID-19 like a health and safety issue. Ask whether it's possible for your business to have social distancing? Can you build in contact tracing tools or mechanisms to keep track of your supply train and customers? Help us get ready as a nation for the marathon we must all run together."