Ardern said the level 3 restrictions, which require everyone to stay home except for essential shopping and essential work, repeating the super cautious approach the country has taken over the past year in stamping out the pandemic.
It was also a positive that all three cases were in the same family and not in the community. "But of course, we will and we have looked at what those exposure sites are in New Zealand and we will be looking at that for anyone coming across the border from New Zealand", he said.
Supermarkets and petrol stations will remain open so there was "no need to rush out to get any essential items".
People board a bus in Auckland.
"It would be much easier if she was a frontline border worker and had regular contact with returning travellers then you'd feel there was quite a plausible mode of transmission into that household".
The rest of New Zealand will also be placed under heightened restrictions although will not go into lockdown, Ardern said.
New Zealand's greatest vulnerability has been at the border.
She said she doesn't want people to "clog up the system".
Director-General of Health Ashley Bloomfield said the vaccine comes in vials that can contain up to six doses.
He described the cases as new and active.
The podiums Ardern and Bloomfield stand at have been moved two metres apart from one another.
Health authorities are still working to find out whether the cases involve one of the new highly infectious variants and how the family contracted the virus, Ardern said.
Officials are in the process of figuring out if the family - who are moving to the Jet Park MIQ facility - has infected anyone else.
"The most important lessons we've learned from the times that we have stamped out flare ups successfully before, and from cases we've seen overseas where outbreaks have gotten away is the need to go hard and early".
Ardern was in Auckland for the Big Gay Out today, but flew back to Wellington to be briefed.
"There are still a lot of questions here. this is a precautionary measure", Mr Hipkins said.
There are still a number of "pieces of the puzzle" that officials need to collect, such as how the mother who worked at LSG Sky Chefs became infected.
Although the airport seems a likely source of infection, Hipkins said officials would seek a definitive answer as to where the infection came from and hadn't yet ruled anything in or out.
Speaking to reporters about 1.30pm, he said no emergency Cabinet meeting had been called tonight.
Hipkins says more information on the Covid-19 cases would be needed before a decision on Covid-19 alert levels might be made.