Eighty-nine people have been identified as close contacts of a person who attended a North Shore gym before they tested positive for Covid-19.

All of those gymgoers are being advised to self-isolate for two weeks in case they too have become infected with the virus.

Les Mills Takapuna has carried out a number of "deep cleans" at the site since being told by health authorities that one of its members had tested positive in the last few days.

The infected member attended three classes last week - two on Wednesday and another the next morning.

On Wednesday, the member was there between 5.15pm to 7.15pm - attending the RPM Sprint class that started at 5.30pm and a Body Combat class that started at 6.15pm.

They also attended a Body Combat class the next morning that started at 9.15am. They were at the gym between 9am and 10.15am that day.

Every single piece of equipment - from weights to large workout machines - at a North Shore gym has been thoroughly cleaned after a member later tested positive to Covid-19.

Despite being advised by the Auckland Regional Public Health Service that it was safe for the club to open to the public because of its ongoing cleaning regime, the gym has carried out an "additional full deep clean" at the site and conducted anti-viral fogging treatment too.

"We go beyond the Ministry of Health's guidelines for cleaning and disinfecting where a confirmed case of Covid-19 has been identified," the club says on its website.

"Our deep clean is from floor to ceiling and including all equipment - every weight, every bar, every bench, every surface and all equipment as well as changing rooms, wet areas, common spaces and shared facilities.

"They are all cleaned with hospital grade cleaning products to ensure our facilities continue to be safe to use."

The gym remains open.

But anyone who attended the same classes as the person who tested positive later is being told they are officially regarded as a close contact and should self-isolate for 14 days.

Gym case could 'kick off' cluster again

All members who attended those classes are being considered as being "at a greater risk" of becoming unwell, the gym has been advised.

Physics professor Shaun Hendy, of the University of Auckland, told Radio NZ the gym case could lead to the current Auckland cluster growing yet again.

"Our modelling shows that we could have this long period where we gradually get in to a few zeros, a few days with one case or so before eliminating.

"But there's also still the possibility that the cluster could kick off again. The modelling shows both scenarios are possible."

He said going to the gym was a "high risk activity" as people were breathing hard and close to others indoors.

Regarding today's much anticipated announcement about a potential move of alert levels, Hendy said he did not think restrictions should be eased today.

Les Mills head of club operations, Brett Sutton, told the Herald they had stringent tracing systems in place for all member visits and had been able to supply that information to ARPHS quickly.

"We've supplied information quickly to health authorities and we've also been in direct communication with our members," he said.

The official advice for affected gym members is to call Healthline, which operates 24/7, on 0800 358 5453 and to arrange to get tested for the virus.

Anyone who was at public gym at any of those times - but was not at any of the classes mentioned - are considered casual contacts and do not need to self-isolate unless they become sick.

The gym says anyone who is required to self isolate can contact the gym to place their membership on hold under the "Special Covid-19 pause".