There are eight new cases of Covid-19 in New Zealand - one in Christchurch, two in Waikato and another in Invercargill, Director-General of Health Dr Ashley Bloomfield says.

Four of the new cases are in Auckland.

That brings the total of confirmed cases to 20 since the coronavirus outbreak began.

Details for each case will be on the Ministry of Health website, including flight information, once it becomes available.

Bloomfield understood all eight new cases were Kiwis returning from overseas.

All those he had details on had been in self-isolation.

They were aware of the symptoms and did the right thing and became symptomatic, he said.

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.

• Four new cases: Dunedin school to close for 48 hours
• Three tourists up for deportation for failing to self-isolate
• 'Imminent' roll-out of routine testing to see how widespread Covid-19 really is
• Coronavirus: Travel details of latest confirmed cases revealed

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.

'No evidence of community outbreak'

There is still no evidence of community outbreak, he said.

The risk still appears to be low due to border restrictions. "It is something we are very very alert for" which is why testing is still high.

"We expected more cases, and it's most important that we identify," and contact close contacts to prevent further spread, Bloomfield said.

The new cases reinforce the importance of border restrictions. All were from overseas travel.

"These restrictions are not retrospective but I urge others who have arrived earlier from overseas to voluntarily self-isolate," he said.

"Contact tracing will be underway on any relevant flights for those new cases." That covers two seats in all directions.

Healthline will also have the seat numbers and can advise anyone on the flight whether they are considered a close contact.

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.

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.

PM on the new cases

Prime Minister Jacinda Ardern said the eight new cases of Covid-19, all of them linked to overseas travel, was a timely reminder of the importance of the new travel restrictions.

People who had recently come to New Zealand in the last two weeks should be self-isolating, she said, even though the new travel restrictions only came into force this week.

She said further guidance on public gatherings would be put out in the next 24 hours.

Earlier she said that gatherings of 500 people, indoors or outdoors, should be cancelled.

"We need New Zealanders to be prepared," she said.

"This is not a time for panic. It is a time for preparation."

She said everyone should talk to neighbours and extended family about access to resources.

Australia had banned gatherings for more than 100 people, and Ardern said New Zealand was looking at what was happening overseas - New Zealand's guidance would be announced in the next 24 hours.

She said people should be exercising social distancing, even on public transport.

Australia had banned gatherings for more than 100 people, and Ardern said New Zealand was looking at what was happening overseas - New Zealand's guidance would be announced in the next 24 hours.

She said people should be exercising social distancing, even on public transport.

She welcomed Australia putting New Zealanders on the 'do not travel' list.

She would not comment on whether the Government would bail out Air NZ>

She said there were "very few reasons" New Zealanders needed to travel overseas at this point.

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 authorities were pleased with the level of compliance and that the restrictions were being taken seriously.

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's spot checks

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."