The coolstore employee who tested positive for Covid-19 worked directly with frozen food but his boss says consumers shouldn't be alarmed.

The Americold worker is one of four people who tested positive on Tuesday, but he had been on sick leave for nine days before getting his results back, and didn't have any contact with the public when he was at work.

Americold NZ managing director Richard Winnall told the Herald the man worked in a role where he handled frozen food that was destined for grocery retailers and food service companies.

However, he would have been wearing PPE gear and gloves as part of his handling of those products. He would also have been wearing cold temperature clothing, like a freezer jacket and pants, and possibly a beanie.

In addition to the PPE Winnall said all of the items the man would have handled come with several layers of packaging that are removed at various stages. That means the goods consumers pickup off the shelves are in wrapping that hasn't been touched by anyone in the coolstore.

"So in my opinion transmission (from him to consumers) is improbable".

Americold's managing director Richard Winnall doesn't think consumers have anything to worry about. Photo / Americold

The Mt Wellington coolstore was closed on Tuesday night after the company was informed the man was likely to have Covid-19. His 26 colleagues are now being tested and it's unclear if any of them are among the four new probable cases that have been identified by the Ministry of Health this afternoon.

Winnall said the man's position at the company meant he didn't leave the office or interact with the public and he had not been in contact with employees at any of the three other local branches.

Director general of health Dr Ashley Bloomfield said while the index case for the new outbreak was a man in his 50s, it was still unclear how he became infected.

Bloomfield said surfaces at the coolstore will be tested to see whether freight or something else may have been the origin.

"We do know from studies overseas, that actually, the virus can survive in some refrigerated environments for quite some time," he said.

"We start by looking at all the options and ruling then out, and that's the position we're in at the moment."

Winnall said the majority of the frozen goods are locally produced but there probably were some imported products too.

While admitting he was no expert in the science of transmission he said he wasn't aware of any international examples of it happening via frozen foods.

"In regards to the idea the virus can live on the product... I have seen no evidence it can be a transmission point."

Testing at the coolstore hadn't started this afternoon and he wasn't sure when it would happen.

The company has also been asked to close another branch it has near the airport.

He said that branch did not have any direct links to the airport and the sick employee had not been there so he assumed it was a precaution solely based on the proximity to the airport.

"We are double guessing a little bit on the motives to closing it. It just happens to be nearby, there is no direct relationship with the airport."

Winnall said the company has been in contact with the infected man and he was "doing okay". Support was also being offered to other employees.

Infectious diseases expert Dr Siouxsie Wiles said it was too early to know if the man had caught it from work or if the virus had been brought into the country on frozen goods.

She said there had been a case in China recently where the Covid was found on frozen seafood so it wasn't impossible it could be on frozen goods here.

"At the moment it has shown to be on some frozen things in other countries but it's a rare thing and hasn't been reported on a lot."

Wiles said genome sequencing would hopefully be able to provide more answers, especially if they were able to find a match to any samples in the coolstore.

She said matches on somewhere like the man's desk could have come from him taking it into the office but if there was a match somewhere else in an area he hadn't been - or an item he hadn't touched - then it would suggest he picked up the virus from work.

The Prime Minister had indicated results from such sequencing testing would hopefully be known within 24 hours.

Four members of one family have tested positive. Here's what we know about them:

• The index case - the first case that was identified in the family - was a man in his 50s who lives in South Auckland.

• The man was tested on Monday and again on Tuesday when he tested positive after being symptomatic for five days. He had not travelled and it is unknown where he picked up the virus.

• Three other members of his family also tested positive late on Tuesday.

• Two workplaces are linked to the family. One is a Finance Now where 130 people are being considered close contacts.

• The second workplace is Americold in Mt Wellington where one of the four family members works. He had been off sick for nine days. His 26 other colleagues are being tested. A second branch based near the airport has also been closed today and 20 staff there are also being tested.

• Four members of the family travelled to Rotorua on Saturday. Two of them, including a woman in her 20s and a preschooler, have tested positive. They stayed at the Waiora Lakeside Hotel from August 8-11. They visited the Skyline Gondola and Luge on August 9 between 4-6pm and the Heritage Farm and 3D Art Gallery on August 10 between 3-4pm.

• One of the four people visited Westview Medical Centre in Glen Eden where they were tested by a GP. They also visited the Westview Pharmacy. The entire centre has been closed until Monday 17.

• A child from the family attends Mt Albert Primary School which is now closed for 72 hours. The child, who had not attended school this week, has tested negative.

• A further four people are being treated as probable cases after showing symptoms. Two are relatives of the family and two are co-workers. They include three adults and a teenager.