Prime Minister Jacinda Ardern is asking every Kiwi who has returned to New Zealand in the last fortnight to self-isolate, even if they arrived before strict travel restrictions came into force.
She has also issued a stern caution about a possible outbreak of Covid-19, saying New Zealanders need to plan for scenarios such as working from home and self-isolating, and to cancel all non-essential travel.
"This is not a time for panic. It is a time for preparation. I ask everyone that they think about that for them and their family," Ardern told reporters this afternoon.
Her comments come as eight new coronavirus cases, all believed to be New Zealanders returning from overseas travel, were announced today, bringing the number of confirmed cases to 20.
Ardern said this underscored the importance of people arriving in New Zealand to self-isolate.
But she added that anyone arriving in the past fortnight should also self-isolate, even though the requirement to do so only came into force at the weekend.
"Many came in after those border restrictions. Many came in before there was an escalation in cases overseas. They may not have known or believed themselves to be susceptible until they have tested positive.
"This is about looking after those individuals interests, but also of their community.
"If you arrived before those border restrictions [came into force], seeing out the balance of your 14 days in self-isolation is the sensible, safest and best thing you can do for the community around you."
The Government's plan to contain the spread of the virus seemed to be working so far, but Ardern said there will be more cases and New Zealanders needed to be prepared for a wider outbreak.
"Think about Covid-19 in the same way you do for Civil Defence emergencies. Prepare a plan for you and your family."
That included thinking about how to work from home, or how to get through a period of self-isolation, including how to access all the resources you might need.
Ardern welcomed Australia adding New Zealanders to its "do not travel" list, noting the travel advice for Kiwis was similar.
"We have simply given the advice for Kiwis not to travel. Get rid of all non-essential travel.
"There's very few reasons I would have thought anyone would consider travelling at this point."
Ardern has already banned all social gatherings - indoor or outdoor - of more than 500 people, except for school events, and would be giving more guidelines for smaller gatherings within 24 hours.
'No evidence of community outbreak'
Director-General of Health Dr Ashley Bloomfield told media earlier today that there were eight new cases of Covid-19 in New Zealand - one in Christchurch, two in Waikato, one in Invercargill, and four in Auckland.
That brings the total of confirmed cases to 20 since the coronavirus outbreak began.
All those he had details on had been in self-isolation.
All eight, as well as a Logan Park student from Dunedin who tested positive, had their infections detected yesterday - 620 tests were processed yesterday.
Asked if the increase in cases proved NZ should have been testing more people, he said instead it was the case that more people coming from overseas were coming from Covid-19 hotspots. Some had come from Europe, some from Australia and some from the United States.
Information was being sought on how many Kiwis were returning from those areas, but Bloomfield said the numbers were dropping quickly as travel dropped off.
He was not aware of any new cases of travellers being placed in forced self-isolation, following the two tourists who had arrived from South-East Asia previously reported.
There is still no evidence of community outbreak, he said.
The risk still appears to be low due to border restrictions.
"These restrictions are not retrospective but I urge others who have arrived earlier from overseas to voluntarily self-isolate," he said.
Healthline will also have the seat numbers and can advise anyone on the flight whether they are considered a close contact.
There are 30,000 swabs for Covid 19 being distributed around the country, and community testing is expected to start soon to gauge how widespread Covid-19 has become.
Bloomfield did not know the number of ventilators in the country but that information is being collected.
In addition to those in intensive care units, there are ventilators in operating theatres and sometimes in post-operative areas which can potentially be used.
However, ventilators are only useful if someone has the right training to use it.
DHBs are working with the Ministry of Health to collate that type of information which is not held centrally.
Stopping elective surgery was one option to make sure there was flexibility in the system. Private hospitals are also being contacted to see what capacity they have if necessary.
The important thing was to make sure the peak of the disease did not exceed the health system's capacity, Bloomfield said.
Regarding the WHO's advice that paracetamol is preferable to ibuprofen, he said he did not have specific concerns but said the WHO was probably referring to the side effects of ibuprofen which could be damaging for some older people, unlike paracetamol.
When will the pandemic peak?
Asked if there was modelling advice suggesting community transmission was likely to start early next month and peak in August, Bloomfield said that would be accurate if the disease transmission was thought of as a single wave.
But a new model that had come through overnight looked at what could be done to prevent that peak.
Even if the peak is flattened, the health system's capacity would still likely be exceeded, he said. Instead, it appeared a series of small peaks over a longer period, with stringent controls to ensure the system's capacity was not exceeded, would be the most successful strategy.
"The challenge here ... is you need to think about what ... we might need to do in two weeks' time, and we do it now." New Zealand had done this well so far as it had been able to look at what had succeeded in other countries and apply it early here.
School closures
Regarding the closure of Logan Park High School in Dunedin, he said the school was working closely with public health officials.
It was initially closed for 48 hours but given there are around 150 close contacts who have self-isolated, and it is the first such case in a school, all 150 of those people will be tested.
Tests won't all be back until Friday, so the school will remain closed until after the weekend.
All close contacts will still need to self-isolate for 14 days because they may still be incubating the virus, he said.
Bloomfield said there were no other schools that might be involved, but there could be new information coming in on the eight new cases.
Traveller self-isolation checks
Police have been visiting a random sample of travellers to check they are self-isolating as required. About 50 people have been visited throughout the country.
Police made contact with 41 people yesterday, and another 3 are being followed up today as they could not be reached at the time. More visits will be conducted.
Bloomfield said the ministry was looking "very carefully" at Australia's plan to stop gatherings of more than 100 people.
He understood all eight new cases were Kiwis returning from overseas.
The early start to the flu vaccine campaign was announced today. An extra 400,000 are available this year - a 30 per cent increase.
It's most important to protect people who could be hospitalised if they have the flu - that is people over 65 or those with pre-existing conditions. They will be the ones prioritised over the next four weeks.
The flu vaccine does not help with Covid-19 but will help keep the strain off the health system.
He said last night's party was a St Patrick's Day gathering involving uni students. The MoH has given Cabinet further advice around mass gatherings - stopping such gatherings is an important part of preventing community transmission, Bloomfield said.
Bloomfield was joined at the update by the Ministry of Education's Secretary of Education Iona Holsted.
Yesterday four more cases were confirmed - a father and son in Wellington who had returned from the United States and a Dunedin man in his 40s who had travelled from Germany.
Last night his son also tested positive.
Logan Park High School in Dunedin is closed for 48 hours from today after the student at the school was confirmed to have the virus.
The school is currently being thoroughly cleaned.
Holsted said the ministry is not currently planning for widespread school closures but is planning for temporary closures - like what's happened at Logan Park.
Children should continue to attend schools and ECEs, she said.
However schools and ECEs should continue to prepare for distance learning - not because of closures but because of self-isolation.
The MoE is not considering bringing forward the April school holidays, Holsted said.
She said telecom providers were looking at support for schools that might have children in isolation. That included extending connectivity for some areas.
Once that was dealt with the MoE would be looking at where more devices were needed.
On reports of a large party being held last night - despite Logan Park closing - she said closing schools did not stop people meeting. This showed children would not necessarily be safer if schools were closed.
Police have conducted spot checks on 50 tourists to confirm they are following self-isolation requirements.
"The visits, which commenced yesterday, involved police visually sighting the individuals and asking a series of questions relating to their wellbeing while self-isolating," police said in a statement today.
"Police has made contact with 41 individuals with another three people requiring a follow up today when they could not be reached. Outstanding visits are scheduled to be completed today with more visits to be conducted."
Police said they were pleased with the high level of compliance with "most people taking the isolation requirement seriously".
"Staff have been provided with advice about how to keep themselves safe while conducting these visits. This includes maintaining a safe distance, and carrying out standard risk assessment for each visit."
The Ministry of Health also announced earlier today that coronavirus testing would be rolled out across the country and would be a routine test given at the same time as the flu test.
According to Johns Hopkins University, more than 197,000 cases of Covid-19 have now been confirmed. The majority of these are now outside China. While just over 7,900 people have died, close to 81,000 have recovered.