A third Auckland woman linked to the pair who travelled to Northland, prompting the region to plunge into lockdown, has tested positive for Covid-19.

The Ministry of Health says the new case had been in Northland with the other two women between October 2-8 but wasn't infectious until after she returned to Auckland.

Northland shifted up to Level 3 after a lack of cooperation from the initial case who returned a postive result in Whangārei on October 6.

The second person later tested positive for the virus having been unable to be tracked down by police for several days.

Public health officials have identified three household contacts along with two other contacts linked to the new case.

These additional contacts are a result of a visit to another home in the Auckland area as well as a shared trip to a testing centre.

The Ministry of Health announced 41 new cases of Covid-19 on Saturday, 40 are in Auckland and the other is in Waikato.

Of the cases, 21 are yet to be linked to the current outbreak.