The person who attended three gym classes in Auckland before testing positive for Covid-19 is a healthcare worker at the country's only quarantine hotel.
The Ministry of Health said it was likely the worker contracted the virus at the Jet Park Hotel near Auckland Airport, but exactly how is still being investigated by health officials.
Authorities have urged 89 close contacts who attended the classes on September 9 and 10 at Takapuna's Les Mills to self isolate and get tested.
The person also visited The Warehouse and Countdown in Milford on Thursday September 10.
There are now 177 cases in the Auckland cluster, and tomorrow health authorities will be able to confirm if any of the close contacts from the gym have tested positive.
Les Mills owner Phillip Mills said they follow Exercise NZ's guidelines and more.
The fans are turned off, saunas closed, water fountains off limits and classes are limited to 100 people who have to keep 2m apart.
"We've gone to great detail to make it safe to come into the gyms, from having perspex shields in front of the receptionist, all the staff in masks and having perspex shields between the machines," he said.
"We have really got as good a safety measures as any business in the country, probably better than most. We think this is very important and it's crucial that people are exercising."
Of the close contacts who attended classes at the Takapuna gym last Wednesday and Thursday, 20 were in the Sprint class, while 69 attended Bodycombat.
They have been urged to get tested and self isolate.
Mills said the class teachers were among those isolating.
"We have suggested people wear masks if they will and I think that would be perhaps the next step for the government. We'll see how this one goes."
The ministry is yet to confirm how many of the 89 close contacts have been contacted and are self isolating.
Prime Minister Jacinda Ardern said routine testing of managed isolation and quarantine workers picked up the healthcare worker had Covid-19.
According to the Ministry of Health, the worker has five household contacts, who have all returned negative test results.
A spokesperson for managed isolation and quarantine said health workers at all managed isolation facilities, including Jet Park, did not have access to the hotel gyms.
"We give them guidance on keeping themselves safe outside of work, including asking them to keep records of their movements and close contacts (just like all New Zealanders) while not at work, and when finishing work to have a shower and change clothes before returning to their loved ones," they said in a statement.
"With all these precautions in place, the risks have been assessed as minimal, so they and their partners/spouses and children can follow their normal routines depending on any current alert level restrictions. That includes for exercise."
Those still heading to Les Mills in Takapuna today were not exactly working up a sweat over the risk of Covid, telling RNZ they felt confident about the gym's safety measures.