Dr Ashley Bloomfield says one of the latest Covid-19 cases in the community - a woman in her 20s - had travelled to Rotorua over the weekend while she was symptomatic.
Watch the media briefing here:
Prime Minister Jacinda Ardern and the Director-General of Health along with the Police Commissioner gave a briefing with updates on the new Covid-19 cases and the alert level changes.
The government last night announced that four Covid-19 cases of unknown origin had been found in a family in South Auckland. This prompted a move to alert level 3 for all of Auckland from noon today and level 2 restrictions for the rest of the country.
Restrictions will last until at least midnight on Friday, but experts are warning people to prepare themselves for the possibility they will remain in place longer.
A child who attends Mount Albert Primary School is believed to be involved with the community cases.
People in Rotorua and around the country should seek advice if they have symptoms, Dr Bloomfield says. The woman who was symptomatic was with a child - who later tested positive - and had visited some family and tourist locations during their visit there, he says.
The ministry is working to find out where else she went in Rotorua.
Ardern says the whole country has gone to level 2 because the pair travelled to Rotorua.
- If you have symptoms of the coronavirus, call the NZ Covid-19 Healthline on 0800 358 5453 (+64 9 358 5453 for international SIMs) or call your GP - don't show up at a medical centre
There are testing sites available in Rotorua (on Vaughn Rd) and Taupō for people in the area, he says.
The family are still in isolation at home and the ministry is working with them about possibly going into quarantine, he says.
No members of the family require hospital care at this stage.
The ministry is testing all close and casual contacts of the family that have come into contact with them recently, which the ministry estimates to be 130 people including workplace colleagues.
Three colleagues of one of the new cases and his partner are symptomatic and are isolating, Dr Bloomfield says.
He says there is a finance company and a Mt Wellington cool store involved with the new cases. However, officials are not ruling out that the virus could be surviving in the refrigerated environment and surfaces of the cool stores, which has four locations across Auckland.
The number of confirmed cases remains four at this point, and "a number" of others have been tested but the results of those is not yet known, he says.
The ministry is using genome sequencing on all those who have tested positive to try and track the source of the virus.
Ardern refuted suggestions doing the rounds that the government knew about the new cases earlier than yesterday, she says Dr Bloomfield was first told by the Counties Manukau DHB chief executive and then he told her.
She first learned of the cases about 4pm yesterday after a public event in Whanganui, she says.
Ardern and Dr Bloomfield will provide another update at 4pm.
Follow the latest updates on RNZ's live blog.
Mask supply, testing capacity and impact of level changes
There are 140 people on standby to help from the National Contact Tracing centre Auckland health staff, Dr Bloomfield says.
He says the ministry is prepared to test tens of thousands of people over the coming days and they have capacity to test 12,000 a day.
Testing stations in Auckland will be available in Eden Terrace, Northcote, Henderson, New Lynn, Wiri and Ōtara from 8am or 9am until 5pm or 6pm for seven days a week.
Ardern is asking for only symptomatic people in Auckland to be tested and not clog up facilities.
She says the Ministry of Health is working to scale up its testing capabilities over the coming days.
With news of the aged care lockdown, Ardern said the ministry was working with the sector to ensure staff did not work across different facilities.
Under alert level 3, Aucklanders should re-form their family bubbles like the previous lockdown and the same restrictions apply as last time, Ardern says.
"We are taking a rapid response to break the chain of transmission through contact tracing, testing and the gathering of information.
"I know how hugely frustrating this is for everyone of our team of 5 million."
Ardern says businesses can still trade during alert level 3 as long as distancing is maintained and orders are taken over the phone or online.
People should make sure they keep their 2m distancing when out in public.
The NZ Covid Tracer app has had more than 100,000 downloads overnight, Dr Ashley Bloomfield says, and he encourages more people to do so.
Ardern says the government is seeking advice from the Electoral Commission on what is happening with the election, but there is no update yet.
The Minister of Health and Dr Bloomfield are asking people in Auckland to wear masks if they are out in public either for essential travel or supermarket shopping.
Ardern says they will release five million masks from New Zealand's central supply, and they will be mandatory on flights leaving Auckland.
Chris Hipkins said making mask wearing mandatory for Aucklanders was one of the things being considered.
Police to monitor Auckland boundaries during level 3
From 12pm today, police will monitor nine checkpoints coming in and out of Auckland, five in the north and four in the south, Police Commissioner Andrew Coster says.
Auckland police staff will wear masks when dealing with the public, Coster says. Additional PPE will also be used.
Coster says defence staff will also be working with police to monitor the checkpoints, 40 police staff in total will work at the checkpoints.
He says the powers for enforcement in Auckland will be with police.