There are no new Covid-19 cases in the community, director general of health Ashley Bloomfield says.
He said the new community case from yesterday - which plunged Auckland into alert level 3 and the rest of New Zealand into alert level 2 - was the UK variant.
Contact tracers have identified a link between the two families from the Auckland suburb of Papatoetoe.
All information to date suggests all the confirmed cases are from one cluster.
This was a positive update, Bloomfield said, as it meant there was still only one cluster.
He said there was a "strong" focus on seeing if there were any new cases at Manukau Institute of Technology, where one of the latest community cases studied.
He said at the "very least", people who were there should be at home in isolation.
Bloomfield said the Ministry of Health accidentally made a mistake "when working at pace" in terms of the dates around the Manukau Institute of Technology visits.
The correct times have now been updated, he said.
Prime Minister Jacinda Ardern said there was a possible person-to-person link with the new cases.
"This is good news," she said as it meant a direct picture could be made about how they got the virus.
But she said the potential exposure event over the week was a concern.
Asked if she would consider moving Auckland out of alert level 3 if there continued to be no new cases, Ardern said the UK variant had a "longer tail" that meant there might be more positive tests to come.
Ardern said the advice Cabinet received from the Ministry of Health was for a seven-day lockdown, but all the information was being reviewed on a daily basis.
Ardern revealed Cabinet talked about having Auckland at level 3 and the rest of the country at level 1 but she "didn't want to leave the rest of the country exposed".
Bloomfield said officials were seeing "unpredictability" with this variant.
Asked if he was confident level 3 was high enough, Bloomfield said yes - as long as people followed isolation rules.
"As little human-to-human contact is what we ask for at level 3."
Those in isolation are essentially in "full lockdown".
Ardern said she was advised about the case at 3pm yesterday, but had "very little detail" necessary to make a decision. That came around 6pm.
She said it would have been tough to shut events halfway through.
Big events were staged last night across the country, including the Joseph Parker vs Junior Fa fight in Auckland and a Six60 concert in Hamilton.
Ardern acknowledged the "frustration" of Aucklanders, but said "turning on each other" would not help, referring to the community case who broke isolation rules.
"We are nearly there. In the meantime let's stick together," she said. "We've done it before, we can do it again."
She said a "number of events" had been affected by the new alert levels, she was "devastated for the fans", but Covid meant the events had to be cancelled.
Ardern said people were spreading Covid-19 misinformation.
"It's real," she said.
One thing everyone could do was to make sure accurate information was being shared and the Government would provide experts to help provide correct information.
Ardern said she was keeping an eye out for rule-breakers and the Government was doing check-ins on people isolating, she said.
She said if officials had concerns people were not isolating, they would work with police to ensure they stay at home.
She said the "vast majority" of people have been complying but a handful hadn't and that had "dire consequences".
The last time check-ins were deployed by police was during the August outbreak.
Ardern said, so far, 75 per cent of people who have received Covid vaccines are from South Auckland. These are people who work at the border.
She confirmed when the general vaccination rollout starts: "South Auckland will be first."
She said it made sense the vaccination programme started there as it was higher risk.
Ardern reminded businesses about the wage subsidy and the short-term absence payment. The latter is for people who need to stay home as they have had to stay home.
She called on managers to talk to their staff and make sure they were not meant to be isolating. If they were, she said, they need to stay home.
Ardern said staying home would keep everyone safe, and help ensure New Zealand could move back down alert levels.
On the IRD phone lines and website, Ardern said they would be restored on Monday.
The outage was pre-scheduled.
She said the issues wouldn't change the timeframe on the subsidy scheme.
At the start of the press conference Ardern said New Zealand was seven hours into the new alert level settings.
She warned that "Covid kills people" and the lockdown measures were to save lives.
She asked that anyone who has symptoms and anyone who was at a place of interest to get tested straight away.
She said people must stay home after their test until they had been given the "all clear".
Others were also urged to stay home.
"If you can work from home, please do."
She said New Zealand has beaten Covid before and "we can do it again".
She said the vaccine rollout is happening soon. "We just need to keep going."
Bloomfield said there were more testing stations set up in Auckland and there had been 755 tests this morning alone.
But he called on only people who are symptomatic, and people who were at the location of interests, to get tested.
He said the UK strain had been showing symptoms New Zealanders might not have seen before - such as aches and pains.
"You shouldn't be socialising and inviting friends over," he said, of Aucklanders.
But he thanked Aucklanders for their support so far.
On saliva testing, which National has called to be rolled out around the country, Bloomfield said this was the least reliable test and he backed nasal testing.
Asked if anyone outside Auckland has been told to self-isolate, Bloomfield said no "as of yet".
Bloomfield said there were two other cases in managed isolation today, who tested positive for Covid-19.
Yesterday afternoon's community case, which officials are calling "Case M", was a household contact of a Papatoetoe High School student.
That student had tested negative for Covid-19 three times and was asymptomatic.
Despite this, official health advice was that all household contacts of students should have been self-isolating.
This person – a 21-year-old student – was in the community. On Friday, after he went to the GP to get a test, he went to the gym.
Ardern last night said this was "frustrating" and the person was not following the rules.
But she warned against a pile on, as that might deter others from getting a Covid-19 test.
She did, however, call on New Zealanders to follow the rules "on behalf of everyone".
Speaking to media this morning, Covid-19 Response Minister Chris Hipkins said testing had confirmed the new community case was the more infectious UK strain and he expected there would be more community cases.
Speaking to Q&A this morning, Hipkins said South Auckland was clearly more at risk of Covid-19 and this would be "reflected" in the Government's vaccine rollout plan.
He said after frontline Covid-19 workers had been vaccinated, the Government would be rolling it out to "those who are more at risk within the community".
That would be people with health conditions and the elderly, he said.
He also said the Government was looking into places that had more risks.
"Clearly, South Auckland is located by the big airport where most of the people are coming into the country from. Clearly, that [South Auckland] is a setting that probably is a bit more at risk. I think you will see that reflected in the vaccine rollout plan".
This will come as welcome news to National Party leader Judith Collins, who told Q&A it was "absolutely essential" the people of South Auckland are vaccinated first.
"I think it has to happen," she said.
Meanwhile, long queues on Auckland's roads formed this morning.
At Mercer, south of Auckland, police checkpoints were up and running within minutes of the new alert level activation.
Google traffic maps at 9am on Sunday showed delays and queues forming on State Highway 1 at Mercer.
About five officers were at one motorway off-ramp to stop vehicles and ensure people with travel exemptions were passing through but others were not.
Virtually all drivers were compliant, many even voicing their thanks to the officers.
About one-third of vehicles were being turned away.
Another injured teenager was found on Cottrell Crescent and later discharged.