Jacinda Ardern's extreme Stage Three lockdown after a small surge in coronavirus cases will cost the country $440million a WEEK - with 250,000 forced out of work already

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New Zealand's latest lockdown is set to cost the economy $440million a week but that figure could grow if the outbreak worsens, economists have warned. 

Prime Minister Jacinda Ardern made the drastic move to force New Zealand back into lockdown on Wednesday after four new COVID-19 cases emerged. 

The shutdown is expected to last until midnight Friday but the number of cases are continuing to rise, sparking fears the nation could be hit by a second wave. 

There have been 13 new cases detected in the past 24 hours, all of which have links back to a storage facility believed to be at the heart of the outbreak.

Economists are now predicting the lockdown could continue for weeks, with the government expected to take a cautious approach.

Modelling from the ASB economics team shows the cost of the lockdown would spiral if the measures have to be increased. 

If the entire country is plunged back into Level Four lockdown - the most severe response - about $1.6billion will be wiped from the economy each week, modelling shows. 

Economists predict about 28 per cent of Auckland's workforce - roughly 250,00 jobs - cannot operate under Level Three. 

People queue outside a supermarket in Henderson, Auckland, on Wednesday after restrictions were reintroduced (pictured)

A notice of closure is displayed at an entrance to the ASB Waterfront Theatre during a lockdown imposed due to the coronavirus in Auckland

'Our estimates suggest a modest impact on New Zealand's GDP, but this could easily grow,' ASB senior economist Mark Smith told the New Zealand Herald.

'The more severe and long-lasting the outbreak, and the more difficult to contain it, the larger the subsequent economic disruption and likely cost.'

Ms Ardern used a staggered approach to the lockdown this time around, placing Auckland under Stage Three lockdown for 72 hours and the rest of the country under Stage Two restrictions.

But given Auckland's significant economic weight, the economy will still take a hit, Mr Smith said. 

Auckland has the country's largest population, accounts for about 38 per cent of the country's GDP and about 33 per cent of employment.

As a result the current lockdown is expected to wipe $439million a week from the economy, but if the outbreak escalates and Auckland must be placed under Level Four restrictions the cost jumps to $712million. 

A police officer wearing a mask gets his morning coffee from The Store in Kohimarama as Auckland wakes to a return to Stage Three lockdown (pictured on Thursday)

Police question drivers as they head in and out of Auckland on SH1 north of Wellsford on Wednesday (pictured) amid new Stage Three lockdown

During the first lockdown in March, which was one of the harshest in the world and lasted 51 days, spending plunged and unemployment rose. 

But the economy was showing signs of recovery.

New Zealanders had spent two month enjoying the return of their usual freedoms when Ms Adern reintroduced the extreme measures after after four after new four COVID-19 cases emerged. 

Since then, another four probable cases - and one confirmed in a high school student - have been found. 

Three more staff members at the facility also tested positive for the virus on Thursday, taking the workplace cluster to four. 

Health experts are still trying to figure out the cluster began after 102 days without a single case of community transmission.

They are using genome sequencing - looking at the genetic material, or DNA, of an organism - to track the source of the infection. 

The government has been scrambling to control the outbreak, they are rushing to test about 50,000 people by the end of the week to stop the virus from spreading further throughout the community.

All aged care facilities will close their doors to everyone but staff from Wednesday to keep those residents safe.

'This is tough for people, but it's necessary. We need to protect the most vulnerable,' Ms Ardern said. 

Ms Ardern also urged residents in Auckland to wear a mask or face covering when out in public. 

'If you are in Auckland, please cover your face if you leave home - masks or a bandanna is fine,' she said.

The new outbreak has baffled authorities who were certain the country had eliminated the virus. 

The Prime Minister announced during a press conference on Wednesday morning that the main weapon in her government's response would be testing.

'We are taking a rapid response to break the chain of transmission through contact tracing, testing and the gathering of information,' she told reporters.

Dr Bloomfield said action needed to be swift to avoid a horror second outbreak being witnessed in other countries around the world.

'So, we have seen in other countries, and jurisdictions, like in Victoria, in Hong Kong and in Vietnam, where a resurgence occurs that it is incredibly important to act early.'