Air New Zealand has confirmed that 30 employees in total have tested positive for Covid-19, 25 of whom had recovered.

Not all cases were air crew, and not all were linked to employment at Air New Zealand, the airline said.

There had been concern that the airline was not releasing information about employees who had tested positive for coronavirus, and also concern from some employees about the risk of crew bringing coronavirus into the country.

Unlike passengers, Air New Zealand crew did not have to self-isolate when returning to New Zealand after working on international flights under coronavirus alert level 4.

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SUPPLIED Air New Zealand says 30 employees in total have tested positive for Covid-19, 25 of whom had recovered.

"Air New Zealand continues to strictly adhere to the Ministry of Health guidelines for air crew and has not had a positive case in the past 12 days," an Air New Zealand spokesperson said.

"Just one positive case has been confirmed since 1 April. Our medical team are actively managing all cases, providing assistance to those impacted and advice to our employees on how to minimise the risk of contracting Covid-19."

All crew returning from Los Angeles have been required to self-isolate for 14 days after the airline identified in late March that layovers there presented a slightly higher risk.

Out of around 3000 cabin crew at Air New Zealand, 27 had been identified as being a 'close contact' on the basis they worked on a flight that included a passenger with a confirmed or probable Covid-19 case, the airline said.

All of those people had completed their self-isolation without illness.

An Air New Zealand steward was linked to one of the largest coronavirus clusters in the country, a wedding at Bluff, but showed no symptoms at the event and said he had followed appropriate health measures at work.

On Wednesday, Director-General of Health Dr Ashley Bloomfield said Air New Zealand was reviewing recent cases and what the current risk was for Air New Zealand staff, particularly when they were on down time.

There would be increased scrutiny of the procedures in place to help make sure New Zealand was not importing any cases through that avenue.

A group of Air New Zealand cabin crew has been told to self-isolate after returning from a recent repatriation flight to Germany that passed through Vancouver, where some of them may have broken the rules around distancing.

During layovers, crew were required to stay in their rooms at all times, aside from going outside for a walk or to visit a local store for food, because restaurants at many hotels were closed.

While outside their rooms, crew had to stick to to physical distancing rules and wear face masks. Crew also had to follow any local health regulations in the country they were in.

Prime Minister Jacinda Ardern said earlier on Wednesday that there was no exemption for someone who was symptomatic, or who tested positively.

She said the difficulty for Air New Zealand was that international crew could not realistically isolate for two weeks after every flight.

"When it comes to aircrew, of course, you can imagine how difficult it would be to implement a regime where, every time someone went and fulfilled a shift at work, they then had to stay home for two weeks.

"What I want to do, as we get to a position of continuing to see smaller and smaller numbers coming in, and as we see those flight numbers drop, just reassess again that all of the protocols we've got around, alongside health, around our aircrew are appropriate.

"But, to date, they have had exemptions because of the expectations of protections in place for them while they are working," Ardern said.

​Every traveller arriving into New Zealand on an international flight since April 9 has had to self-isolate for 14 days either in a quarantine facility, if they showed coronavirus symptoms, or in an approved managed isolation facility, if they were asymptomatic.