It has become apparent some close contacts of the Mt Roskill Evangelical Fellowship church sub-cluster were not previously disclosed, says Health Minister Chris Hipkins.
A student at St Dominic's Catholic College in Auckland has tested positive for COVID-19 and has been linked to the sub-cluster.
The student was last at school on Friday but left early after starting to feel unwell.
Hipkins said in this case, it appears that it was a close contact of the sub-cluster that had not been previously disclosed. However, Director-General of Health Ashley Bloomfield confirmed later on Wednesday that the student was not a close contact of the cluster or sub-cluster.
"We did identify yesterday, in the cluster of cases announced, that there were a couple of cases that had not been previously identified... it would appear that somewhere along the way, someone has not fully disclosed all of their contacts.
"Obviously this is information we'd have liked to see sooner and we may have had fewer infections as a result had we known about the chain of connection."
Authorities are now investigating whether the failure to disclose cases was deliberate or accidental.
"We've got community leaders in there, we've got police working alongside Auckland Regional Public Health as well, to make sure we are getting all of the information that we need," Hipkins explained.
"That's one of the things that the investigation is looking at now and it will include looking at whether there was a deliberate decision not to disclose, or whether it was simply an oversight."
The minister said he asked health authorities to alert the police on Tuesday, as their involvement will represent the severity of the situation.
He explained that the sub-cluster has been a challenge to work with.
"There are certainly some within the cluster that perhaps don't accept or haven't previously accepted the science involved here," he said, adding they are now being educated on the gravity of the situation.
"It would certainly appear that they were skeptical at the beginning. I think that a lot of work has been done with them since then.
"At the end of the day, any system we have around COVID-19 is going to rely on people doing the right thing, so we are working very closely with this community."
He said that so far all testing indicates that the Mt Roskill Evangelical Fellowship is still a relatively small cluster - however, the thought of people not disclosing contacts and the possibility of other unknown cases in the community is concerning.
"It's the thought that keeps me awake every night at the moment. That's not just with this case, it's with every case."
Hipkins said they are getting close to finding the "outer perimeter" of the cluster and Tuesday presented a slight setback - however, parents should still feel confident sending their children to school.
"Clearly there's been one or two cases where the contact tracing system hasn't identified them, but they were picked up by testing instead.
"So, the backstop of wide testing is picking up the extra cases so parents can have confidence that outside of the schools that have been identified there aren't extra cases that aren't disclosed."
Auckland University microbiologist Dr Siouxsie Wiles told Morning Report it's not surprising to hear some in the community are skeptical about COVID-19, contributing to the spread of misinformation.
"There are very key people in our communities within New Zealand and people in positions of influence who are really trying to disrupt our team of five million by spreading false information about the pandemic," Wiles said.
"If that's the reason why some people are not disclosing contacts or have not been cooperating, we're now going to see the consequences of that."
Wiles said we need to be careful in the way we deal with skeptics.
"If you end up being too heavy-handed, you can reinforce those views so it's very important to work with the community."
She also added it's not a failure of the contact tracing system.
"This is a team of five million. This is about people and it only works when we all do our bit ... it's on all of us to be really mindful about sharing disinformation and talking to people around us who might be having these views."
St Dominic's Catholic College will be closed until at least Monday, September 14. The school and its grounds are closed to everyone except cleaning contractors for 72 hours.
The Ministry of Education are working to identify close contacts of the case. Students are asked to continue learning from home in the meantime.