Masks will be mandatory from about midnight tonight for people visiting essential services, including supermarkets and petrol stations.
"From 11.59pm tonight, it will be mandatory for everyone aged 12 and over to wear a mask when they are visiting any of the essential services that are currently open, including supermarkets, pharmacies and service stations," Ardern said.
Staff will also be required to wear a mask and masks are mandatory and places like bus terminals and in taxis.
"If you are in a place that is allowed to be open to provide services to people, or transport, you must wear a mask," said PM Jacinda Ardern.
"Wearing a mask is an act of care to the people around you."
New Zealand entered a nationwide alert level four lockdown overnight after a case of Covid-19 was found in the community yesterday.
Ardern said 55,688 vaccines were given out yesterday, a new record. Vaccinations have been paused to ensure public safety during the transition to alert level 4.
She said all DHBs would resume vaccinations under level 4 conditions, and in some cases they will resume this afternoon.
The Prime Minister also confirmed the Covid-19 Delta virus at the centre of the outbreak in New Zealand originated in Australia.
She said genome sequencing overnight has confirmed the outbreak is Delta, and is linked to the NSW outbreak.
Ardern said only three positive cases have arrived into MIQ from Sydney since July 1: one on August 9 on their day 1 test, and two on August 14 on their day three test.
They are being genome sequenced as part of the usual processes.
She said there had not been any NSW cases at Auckland Hospital, so they were still looking for the link.
Ardern said everyone who came from NSW and Queensland was compliant with the travel restrictions.
She said despite that, the government was preparing to contact all cases who have arrived from Australia should they find the community case is not linked to the three positive cases from MIQ.
Bloomfield said a further two cases are in the community, bringing the total to seven, after four more cases were found today.
Three cases were found in managed isolation, he said.
The other four cases include a work colleague of the case found yesterday. He has three flatmates including a woman who works at Auckland City Hospital and has been working in recent days. She was fully vaccinated.
Bloomfield said the wife of the original case has returned a second negative test.
As of 11am, Auckland regional public health has identified 16 close contacts, 14 of whom have been contacted and the others are being tracked down.
He said there has been no trouble with compliance from contacts.
Wastewater testing has been taken from Rosedale, North Shore, and more samples are being taken across Auckland.
Bloomfield said some modelling suggested between 50 and 100 more cases and it is very important people not move about.
Ardern said New Zealand only need to look at New South Wales to remind us why it was so important to follow the rules: "[They] today have reported 633 cases, 92 were active in the community while infectious".
"Do vaccines make a difference? The answer is yes, an enormous one. To put it bluntly if you've had the vacine you are less likely to catch Covid-19 and much less likely to get sick or die," she says.
According to the CDC the risk of infection is reduced threefold, but in some cases people who have been vaccinated can still get the virus and spread it.
People who were not home when lockdown began are being asked to return to the place they will be until the end of lockdown as soon as possible.
Ardern said people who have flights booked they are no longer able to use should cancel them, to allow people who may need a spot on a flight to use it.
She said there have been many reports from airlines of no-shows.
Bloomfield said it was very important that people who need acute medical care should receive it.
He thanked nurses who called off their planned strikes yesterday after the news of the outbreak and lockdown.
Ardern said most people are doing the right thing, according to Police Commissioner Andrew Coster. People may be nervous about Delta, but "we can get on top of this, just like we have every other time, if we do it together".
Ardern said there was still a risk to the South Island.
"So long as we are yet to pinpoint the exact source of this case, I cannot hand on heart tell you that the South Island isn't implicated. And so I would rather have more information to assure ourselves of that before we treat the South Island any differently."
She said some people have already been identified from the locations of interest who may be in the South Island.