Northland's positive Covid-19 case tally remains at two despite the national number rising to 155 yesterday.
Forty more positive cases in New Zealand were confirmed as at 10am yesterday in an announcement by Director-General of Health Ashley Bloomfield at Parliament.
That brought the nation's tally of confirmed and probable cases to 155. Within that number, it was announced 12 people had recovered and four had been deemed a result of community transmission - three in Auckland and one in Wairarapa.
The majority of yesterday's announced positive cases were from Auckland or Wellington. None were from Northland.
Northland had its first confirmed case of coronavirus on Thursday - a man in his 20s who returned home from overseas early last week.
The Northlander flew from Paris to Abu Dhabi on Etihad flight EY38, then on to Sydney on flight EY450, and the final leg of his journey to Auckland on Monday was on Virgin Australia flight V0141.
Northland's second case was a woman who had recently returned from Australia and tested positive. The Northlander, in her 40s, flew from Melbourne to Auckland on flight JQ217 on Sunday, March 15.
In yesterday's briefing, Bloomfield said more than 900 tests were conducted on Tuesday, bringing the national total to over 8300.
Regarding about a third of the 40 new cases, Bloomfield said there was a link to overseas travel or to close contacts of an already confirmed case.
Bloomfield said there was a clear consensus among public health professionals and scientists that moving to alert level 4 sooner rather than later gave New Zealand the best chance to break community transmission.
Northland's community based testing centres opened on March 20 and as of 5pm Tuesday, a total of 235 swabs had been taken with an average of 93 people visiting the testing centres per day.
Northland had seven such centres across Whangārei, Kaipara, the Far North and the Mid North, the locations of which could be found on the Northland District Health Board (NDHB) website.
NDHB communications officer Paula Martin said anyone who suspected they might have Covid-19 could come to a testing centre, call Healthline (0800 611 116) or call their GP.
The centres were designed to test all people who had symptoms or had travelled and become unwell/developed symptoms. Symptoms included having a fever or at least one of the following symptoms - shortness of breath, cough or sore throat.
Martin said people visiting testing centres should wait in their car for a staff member to approach them. Test results were expected after five days.
Martin confirmed there would be no change to the testing centres after the lockdown had begun, despite calls from academics to streamline the current testing process.
Dr Ayesha Verrall, an infectious diseases doctor and epidemiologist at the University of Otago, said in a statement yesterday New Zealand needed to make testing more accessible with faster test turnaround times through things such as smartphone apps.
"This means rapidly building our capacity for case identification and contact tracing capacity," Verrall said.
"We should aim to leave the lockdown in one month with the ability to identify and trace the contacts of 1000 cases a day."
Verrall said if the testing process was more streamlined, New Zealand could reflect the success had by China and South Korea in past dealings with large outbreaks.
"If we had better ability to find cases and isolate their contacts, we would be able to manage larger numbers of cases without going into lockdown.
"Building this capacity means we could look to the next 18 months with more confidence that we won't have large outbreaks or be in perpetual lockdown."
On Monday, Prime Minister Jacinda Ardern announced the country was in alert level 3 in response to New Zealand's Covid-19 status and would be moved to level 4 from 11:59pm today.
In a briefing yesterday, Ardern said the underlying principle for alert level 4 was to reduce contact to people to the "bare minimum".
"That's how we will save lives," she said.
Ardern said everyone needed to pay gratitude to those working in essential businesses, "the necessities of life", and to show that by staying home.
"You are literally putting those at risk who have to be there, like our hospital workers."