A cool storage facility in Auckland will be tested for Covid-19, with the possibility that the virus could have travelled into New Zealand on refrigerated freight.

Four cases of Covid-19 were discovered in south Auckland on Tuesday evening, ending a 102-day run of no community transmission.

One of the people infected worked at Americold, a cool store company in Mount Wellington.

Health officials have not ruled out the virus, surviving in a refrigerated environment on freight being transported from abroad, may have then been contracted at the cool store.

Dr Ashley Bloomfield on Wednesday said “environmental testing” of the storage facility would take place as well as looking for transmission between staff.

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

He was unsure if the cool store was receiving international freight that had been refrigerated for its whole journey.

The cool storage facility where the man worked, in Mount Wellington, had been closed down along with three other sites the company had around the city, he said. The 160 staff across all the facilities would be tested for Covid-19.

Americold’s managing director Richard Winnall said the staff member with coronavirus is now at home in south Auckland and doing well.

He works alongside 26 others at the facility.

“Our head of operations reached out to him and his family and they are doing OK. They're overwhelmed at the attention, but doing OK,” Winnall said.

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The employee had been on sick leave for nine days and did everything right, including staying home when he started experiencing flu-like symptoms.

“It was a relatively quick time frame from being told we had a suspected Covid case to it then being confirmed positive,” Winnall said.

“This all happened after-hours and shut down pretty quickly, it was a decisive move.”

Winnall said the ministry then advised the company it would have to close the airport site, not because there was a suspected case, but because of the site's proximity to the airport.

Prime Minister Jacinda Ardern said the surfaces would be tested because, “while we primarily look for human-to-human transmission” they needed to be sure freight wasn’t involved.

Professor Michael Baker, an epidemiologist, said it was an “intriguing idea” that the virus might survived on a surface across the border.

He was not aware of this being documented at all in research.

“In general the role of surfaces for transmitting the virus has probably been overemphasised in the past.

“There’s much more focus now on transmission in indoor environments, and respiratory droplets and aerosols,” he said.

It was poorly ventilated, indoor environments where people incubating the illness came into contact with others that posed the greatest risk, he said.

The first of four cases identified on Tuesday evening was a person in their 50s living in south Auckland. This person worked at a finance company with 130 others, and three people working there were now symptomatic.

The second case, the partner of the first case, was the cool storage worker. A third case, a woman in her 20s, travelled to Rotorua on Saturday with four others on the weekend of August 9.

The fourth case was a pre-schooler who also travelled to Rotorua.