There are 21 new cases of Covid-19 in the community - bringing the total number of people infected in the latest outbreak to 51.

And Prime Minister Jacinda Ardern did not think the outbreak had hit its peak.

Because Auckland is at the centre of the outbreak it was "very likely" restrictions would remain beyond Tuesday, Ardern said.

Cabinet is meeting on Monday to make a decision on the country's alert level 4 lockdown restrictions.

Ardern said she expects cases to rise into early next week before they start to drop.

The virus can continue to spread during lockdown, as has been seen in New South Wales, Ardern said.

Ardern said the 825 cases announced in NSW today was "devastating".

"Reduce down your public contact so we don't end up in a situation like NSW," Ardern urged.

"I want us to get back to levels of freedom," she said.

Ardern said prior to Delta you would not necessarily see whole households of positive cases being infected. However, with Delta this was not the case and accordingly it increased case numbers and projections for cluster numbers.