Health officials are searching for an unknown person who could be the missing link between two infected people in one household.
Director general of health Dr Ashley Bloomfield said two cases in one household had different mutations of the virus, which suggested an intermediate case between the two.
Officials were now trying to find that person, he said.
Bloomfield also revealed at today's 1pm briefing that the Crowne Plaza vaccination centre is a location of interest in the source investigation into unlinked cases - but this is not linked to the MIQ facility at the hotel.
There are 11 new community cases of Covid-19 in New Zealand today - all in the Auckland region.
Bloomfield said there were now 29 unlinked 'mystery' cases under investigation in the outbreak, including six today.
Several new locations of interest have been released as part of a source investigation into unlinked cases - one of those is the Crowne Plaza vaccination centre on August 23 - after the person from New South Wales left the Crowne Plaza.
The locations are • Commonsense Mt Eden, 284 Dominion Rd, Mt Eden (August 24, 3pm to 5pm) • Farro Fresh Mt Eden, 422 Dominion Rd, Mt Eden (August 21, 1.30pm to 3.30pm) • Federal St carpark, 65 Federal St, Auckland central (August 23, 5pm to 7pm) • Hertz Auckland, 154 Victoria St West (August 30, 1.2pm to 3pm) • Crowne Plaza vaccination clinic, 128 Albert St, Auckland CBD (August 23, 4.30pm to 7pm)
Bloomfield said the Crowne Plaza location of interest was not related to any of the people in MIQ there, because the facility was emptied on August 21.
On those new locations of interest, which date back two weeks, Bloomfield said health authorities were trying to find how the two cases in question had picked up the virus and whether there was an intermediary between them.
The cases in question had only just tested positive, Bloomfield said.
Anyone who visited these locations at the affected times is being urged to get a Covid test immediately but is not required to self-isolate unless symptomatic.
Of the unlinked cases, there was a small number investigated very thoroughly, including two at Middlemore Hospital, Bloomfield said.
Of yesterday's cases, 12 were household contacts and just one was infectious while in the community.
Asked what impact the mystery cases had on alert level decisions, Deputy Prime Minister Grant Robertson said Cabinet was looking for the links, but if testing was high and case numbers were coming down, there was some reassurance that there were no undetected chains of transmission.
Robertson said if there was a high number of mystery cases, that made a decision more difficult.
Robertson said getting tested was one of the things taken into account in Cabinet decisions around alert levels.
He encouraged people to get tested over the weekend ahead of Monday's decision.
More than 14,000 Covid-19 tests were taken yesterday - nearly 8000 of those in Auckland.
There had been 9000 tests per day in Auckland over the last few days, at essential workplaces and in pop-up stations in some communities.
Bloomfield said at this stage of the outbreak cases were popping up in the tail, and so a lot of effort was going into checking for those chains of transmission.
Testing in Auckland was now a mix of surveillance testing at essential workers' workplaces, as well as testing in communities to check people who may not be showing symptoms, Bloomfield said.
This weekend was critical for high testing, Bloomfield said, adding there were 23 testing sites across Auckland open today.
Work was underway to increase testing of essential workers and people working around the border boundaries.
Bloomfield said a number of businesses had been asked to take part in surveillance testing and urged them to take part in that.
On the economy, Robertson said they were aware of the difficulties facing businesses currently. In particular, those in Auckland were "doing it tough" for the rest of the country, he said.
The second payment of the wage subsidy remained open, and if Auckland stayed at level 4 or 3 next week that would trigger another round of wage subsidies.
More than 400,000 wage subsidy applications had been approved, and more than $2 billion had been paid out under it. A second round of resurgence support payments would also open, Robertson said.
Applications would begin next Friday, and be available until a month after the country returned to level 1.
Businesses would need to demonstrate a 30 per cent drop in revenue over a seven-day period.
This could cost up to $430 million. There would be further assistance after that package too, Robertson said.
The payment is different to the wage subsidy scheme and is a grant to help cover fixed costs and overheads faced by businesses.
A further two rounds of the grant would be available - paid out every three weeks.
Robertson said overall there had been more assistance given this alert level 4 period compared to last time.
Asked about the changes to visitor policies at Auckland Hospital, Bloomfield said the changes had been sent to unions for feedback before being finalised.
He said the main principle was to protect visitors as well as staff and patients.
On the 250,000 doses of vaccine from which arrived from Spain this morning, Robertson said there was a big focus on Auckland for the rollout, but the plan was for a national rollout.
He said there was no shortage of vaccinations in Auckland - and stressed that people could get a vaccination this weekend if they wanted to.
Robertson said the surge in people getting vaccinated had come during alert level 4, when it was a major focus. That had dropped off a bit since most of New Zealand dropped to level 2.
Bloomfield said it would also slow down as more of New Zealand got vaccinated, but there were plenty of opportunities to get a vaccination around New Zealand.
On business assistance, Robertson said there was no consideration to changing the criteria for the wage subsidy scheme. it will no longer be available once Auckland drops to level 2.
Robertson said the Government was not in a position to cover the wage bills for all businesses indefinitely - and offering the resurgence payment was a way to keep offering support.
He said Delta Level 2 was providing more difficulties for some businesses compared to the old level 2, but the resurgence payment could be spent on whatever the businesses believed was needed and was "the appropriate" response.
On the latest Middlemore case, Bloomfield said the police involvement was because the patient had self-discharged, so police were used to find her after the test came back positive. Police had also been at her address earlier on a different matter.
Bloomfield said the woman had been honest about her symptoms, and the test was done as part of surveillance testing.
On a vaccination passport, Robertson said there was a "conversation underway" on whether a vaccine pass would be used for access to different venues - such as restaurants or other venues in the future.
He said some employers were also introducing staff requirements for vaccinations.
On mandating vaccines for different workforces, including the health workforce, Robertson said work was underway on vaccine issues and "it was an ongoing conversation" about whether that would happen in the health workforce. That decision had not yet been made.
Asked if the re-opening plan was being delayed, Robertson said that work was still underway. A pilot to trial self-isolation for some travellers would still go ahead later this year. However, he said in each outbreak more was learned, and what impact levels of vaccination had.
"When it comes to Reconnecting New Zealand, that is still the plan, that is what we are working towards."
He said the immediate focus was on dealing with the outbreak.
On the introduction of new Level 2 rules at the last minute, he said the Government had done planning for an outbreak, but when it came to an outbreak they had to listen to health authorities and adapt accordingly.
"What we are doing here is following the advice we get."
On hopes for Auckland coming out of level 4, Robertson said he'd learned to wait for the latest advice before speculating on what the chances of an alert level change might be.
But Cabinet would be looking at overall case numbers, whether they were connected, whether they could be comfortable that there were no chains of transmission that they did not know about.
The extra Pfizer supplies were sourced from Spain in a Government deal announced yesterday to keep up with surging vaccine demand.
Earlier, the Countdown supermarket in Auckland's Manurewa was closed for deep cleaning after a positive case visited the supermarket yesterday afternoon.
A staff member confirmed they were closed this morning, but are due to re-open this afternoon.
A Countdown spokeswoman said: "We're following the advice of the health authorities and any of our team who were working at the time of the visits are self-monitoring for Covid-19 symptoms for 14 days after the exposure and will get tested if they develop any symptoms.
"None of our team are required to self-isolate and the store has reopened."
On Thursday just 13 new cases were revealed, continuing a steady decline over the past week.
Testing numbers have also dramatically increased as authorities work to stamp out any risk of undetected community spread.
Experts suggest drop in alert levels could be on the cards
Experts say all things going well the virus could be again eliminated in the next few weeks, and more positive news could point towards dropping alert level in Auckland come Cabinet's meeting on Monday.
"Sometime over the next couple of weeks, we will eliminate it," University of Auckland Covid-19 modeller Shaun Hendy says.
He told TVNZ's Breakfast that the system and people working on the frontline - essential workers and medical staff carrying out Covid tests, for example - had done "an incredible job" that was now reeling in results.
He said it was "certainly possible" that Auckland could drop down to level 3 as early as next week.
New Zealand was seeing the tail-end of this current Covid outbreak, he said.
He acknowledged that even he was surprised - as were other Covid modelling experts - at the positive signs that New Zealand was about to eliminate Covid in the community again.
Meanwhile, achieving the highest possible vaccination rate is "absolutely critical" to any plans to start reopening the borders, says a public health expert.
That task will become easier this morning when an extra 250,000 Pfizer vaccines are due to arrive from Spain, followed by an even larger shipment due next week from a different country.
The extra supplies are in addition to the 10 million originally purchased directly from Pfizer.
