While it's expected that Aucklanders will likely stay in lockdown for longer than three days, a worst-case scenario would mean it could be seven weeks, a top scientist warns.

Epidemiologist Michael Baker told the Herald it all came down to determining how far this outbreak had already spread and if a direct link to an overseas case could be identified.

"You would expect a longer lockdown would be more likely. The most positive outcome is if contact tracing identifies a clear line of transmission from an imported case or someone working at managed quarantine," Baker said.

"If the direct line to imported cases is established quickly that's very helpful and then it's finding out the extent of infection among the contacts, if some of them are infected then it's working out the extent of infection among their contacts and so it goes on."

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Baker said the extreme scenario would be that New Zealand would go back to the situation in March when the virus was extinguished after five weeks at level 4 and then two weeks at level 3.

"I don't think anyone is imagining that will be necessary this time around but if you are taking the extreme range of possibilities we know from experience in March that it was very effective."

Baker said the wider the outbreak and the more time it took to contact trace, the longer people will be in lockdown.

Professor Michael Baker Department of Public Health, University of Otago, Wellington. Photo / File
Professor Michael Baker Department of Public Health, University of Otago, Wellington. Photo / File

He said in order for the Government to be satisfied to make a call on how long lockdown would go on for, the following needed to happen:

• Aucklanders who are sick getting tested immediately - this will help provide vital information on the extent of the outbreak.

• Finding out how extensive the infection outbreak is among the current community-transmitted cases.

• Finding out if there is a direct line of transmission from the community cases to an overseas case.

Baker said if a link to an overseas case could not be found then that suggest there may be lines of undetected transmission hidden in Auckland, which may take longer to get to grips with.

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"We need to understand how extensive this outbreak is to work out how manageable it is."

Professor Shaun Hendy, a physicist from Auckland University, echoed Baker's comments, saying people should prepare themselves for the possibility that restrictions will stay in longer than three days.

"This initial period is to try to give us a handle on how big the outbreak might be," he told RNZ's Morning Report.

"We haven't identified the links or the chain of transmission back to the border, which is the most likely route of entry for these new cases.

"If we can identify that, then that possibly gives us the chance of a more localised and shorter lockdown.

"If we're unable to do that people should be preparing themselves for a longer lockdown period."

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Hendy said there was a likelihood it has got out of Auckland as someone in the chain of transmission could have travelled outside the area.

"I think people around the country should act as if the disease is present in the community."

Auckland back into lockdown

Auckland moves to level 3 at noon today for three days, until midnight on Friday, after a community outbreak of Covid-19 was confirmed last night- the first in more than 100 days.

Four members of a South Auckland family have tested positive and health authorities are racing to find the source.

Everyone working at the border or in managed isolation will be swabbed and there will be mass testing across the city. Two pop-up centres are opening this morning in Ōtara and New Lynn.

The rest of New Zealand is entering alert level 2 from midday today for three days, also until midnight on Friday.

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Covid19.govt.nz: The Government's official Covid-19 advisory website