Auckland has been at alert level 4 since midnight on 17 August after an outbreak of the Delta variant of Covid-19.

Ardern says today there are 33 new community cases to report, but says only one of them is currently unlinked.

"Likewise of the cases reported yesterday, just one remains unlinked to the wider outbreak at this point."

She says this does not mean the collective efforts of New Zealanders have not been making a difference.

Surveillance testing of healthcare workers and essential workers has also not identified any tramission.

"It's also clear there is not widespread transmission of the virus in Auckland."

The rest of the country has moved back down to level 2, but experts have said Auckland is likely to remain at level 4 a bit longer due to mystery cases in the community.

That includes University of Otago epidemiologist professor Michael Baker, who says today's Covid-19 numbers support the argument for Auckland staying at alert level 4 for at least another week.