Two people in Christchurch who have returned positive Covid-19 tests had not been using the contact tracing app regularly, it has been confirmed.
And one may have been infectious in the community for almost two weeks.
The Ministry of Health was notified last night that there were two people in Christchurch with Covid-19.
They are both in the same household.
Covid-19 Response Minister Chris Hipkins said one had travelled from Auckland on October 15 and infected a second person in their household.
Both people - in the same family - are both unvaccinated.
The first case returned a negative test before coming to the South Island but later became unwell.
The local public health unit is gathering information from the cases to identify close contacts and exposure events, including any locations of interest.
They have been in contact with at least one other household.
The ministry will undertake a public health risk assessment of the situation this morning and a further update will be provided after that.
Covid-19 Response Minister Chris Hipkins said earlier this morning that he had not ruled out a snap lockdown in a bid to contain the spread of the deadly Delta variant.
However, he later told the AM Show though that it is unlikely Christchurch would move alert levels.
He said the these cases could have well been infectious in the community for a period of time and while the extent of their movements were largely unknown interviews were ongoing.
Hipkins said the person travelled to Auckland for an authorised trip that involved the care of a child.
"This is the reality we are in in New Zealand, Covid-19 Delta is here, it is in the country.," he said.
"There's no way to guarantee the virus won't make it's way out of Auckland."
Hipkins said it was a question of when, not if Delta made its way around the country.
He was notified about the Christchurch cases at about 10.30am last night.
A decision on Christchurch is expected at 1pm.
He took the opportunity to once again call on the public to get vaccinated.
He said it was now not if the virus would get to those unvaccinated, but when.
"Covid-19 is on our doorstep," Hipkins said.
"Help us get those high rates of vaccination. It's very safe to be vaccinated. You're far less likely to get sick from Covid-19 if you are vaccinated."
Christchurch Mayor Lianne Dalziel said she woke up to the news this morning like everyone else.
"It was a bit of a shock to the system. It's not the news I wanted to wake up and hear," she said.
Dalziel said it is a reminder of just how contagious the virus is.
"It is just a huge reminder to be incredibly vigilant about using QR codes, wearing masks and the significance of getting tested if you have any systems, no matter what.
"It's going to be really important to get on top of this."
She said It is heartening 89 per cent of Christchurch residents have had their first dose of the vaccine.
"In three or four weeks we'll be at 89 per cent double dose, we're going to be ticking over the 90 per cent.
"The real message is the higher the rates of vaccination, the lower the need for any changes in our alert levels."
Dalziel said she is hoping the two infected people hadn't been out and about very much.
"Everything is going to come down to where the person and the other person have been over the last week.
"I've got my fingers crossed as I'm sure everyone else in Christchurch has."
Epidemiologist Professor Michael Baker told RNZ although Covid-19 is expected to spread throughout the country, the two Christchurch cases were still quite a shock.
The Christchurch outbreak should be manageable if it is just the person who travelled to the city and their household contact, he said.
He said the bigger question was how many other people were now isolating in the South Island.
Baker said a high proportion of people will be asymptomatic or only have a few symptoms so it was critical for people with any symptoms at all to get tested.
He thought Auckland's suppression strategy would start to move across the rest of the country, replacing the elimination strategy.
Hipkins spoke to Newstalk ZB's Mike Hosking about the decision on Christchurch.
When asked if the city could be plunged back to level 4 he said "no not at all".
"We don't have the information to make a risk assessment on that," he said.
"These cases came in late last night, we have got some information on them which means there is obviously questions, we should have answers to those questions later in the morning.
"Both cases are unvaccinated, and I think there is at least one other household that's been identified with close contacts so they will be working to get in touch with them to make sure they are isolating and tested."
Christchurch events up in the air as Delta arrives in town
Christchurch is just weeks away from it's biggest racing events of the year at Addington and Riccarton Raceways.
Addington racing industry manager Darrin Williams said if Christchurch was to move to alert level 3, the racing events would have to run behind closed doors.
Not even the owners will be allowed on-site, just the participants.
Williams said the only thing that would cause them not to race is if the city went into a level 4 lockdown.
"It is certainly disappointing that we have cases in Christchurch, especially if they are unvaccinated and have moved from Auckland," he said.
"There should be strict protocols for people moving who haven't been double vaccinated and aren't proving a clear sample, it puts everyone, not just us, but everyone in jeopardy, I dont know how that's not plain," he said.
Williams said no matter what happens they are prepared to follow any guidelines in place.
