Prime Minister Jacinda Ardern and Director-General of Health Dr Ashley Bloomfield have announced alert level decisions for Auckland and Northland.

Ardern announced on Friday that New Zealand south of the Auckland boundary would be moving to alert level 3 from 11.59pm on Tuesday. Cabinet confirmed this decision today and Ardern says this will be for at least a week, to be reviewed at Cabinet next week.

Northland will likely join the rest of the country at alert level three from 11:59pm on Thursday, Ardern says.

Cabinet has also confirmed Auckland will remain at alert level four until 14 September. Cabinet will consider next steps for the region on 13 September.

Ardern says level 4 "is making a difference".

"The job is not yet done and we do need to keep going."

For Auckland and Northland, Ardern says the cases in Warkworth were found late in the lockdown and were not equivalent to the cases in Wellington, where cases were monitored and did not appear to have spread.

"We just haven't had that level of time for the cases we're concerned about in Warkworth, and with possible contacts beyond. Once we have that same level of reassurance in Northland we feel safe to move alert levels.

She says the government is awaiting test results from wastewater in Northland, and tests from people who were at locations of interest. If they all came back clear Northland could move to alert level 3 at 11.59 pm on Thursday.

"Just an indication here if all those tests come back clear," she says.

Ardern says if New Zealand had not moved into alert level 4, estimates of the number of new cases today could have been about 550.

"The more we do to limit our contact, the faster we will exit these restrictions," she says.

"Auckland is doing a huge service for all of us. And not just now, but throughout this pandemic. It's Auckland that has maintained our gateway to the world, that has done a lot of the heavy lifting in welcoming Kiwis home safely, that has worked hard to keep Kiwis safe when there has been an outbreak. Auckland has done it tough."

She says New Zealand has about 840,000 doses of the vaccine in the country, and has been receiving about 350,000 each week.

"Our planning has been for the programme to administer 350,000 doses per week. We have the supply and infrastructure to do this sustainably over a long period of time."

There has been an increase in demand, she says, and the government is working to reach that but falling short would merely mean falling back to the government's earlier plans.

"If we are unable to do this then the worst-case scenario is we pull back to our planned volumes ... contrary to the reporting, we are not running out of vaccine."

Experts have been welcoming signs that the lockdown has been curbing the spread of the Delta variant, and with new case numbers dropping to 53 today - down from a high of 83 new cases yesterday - the government will have some extra confidence in its decision to lower alert levels in wider New Zealand.

Speaking about today's case numbers, Bloomfield says while it is 30 fewer cases than yesterday, it is just one data point. However, he says 52 percent of the 83 cases reported yesterday were household transmission, and 72 percent did not create any new exposure events.

"So of those cases reported yesterday ... only 28 percent are considered to have been infectious in the community, which may simply have been a visit to a supermarket ... or may be an essential worker.

He says 101 of the total cases are essential workers, just four of them who have been infectious in the workplace and seven who were infected in the workplace.

All of the new cases announced today were detected in Auckland.

Ardern says it's too soon to say if daily case numbers have peaked.

Meanwhile, Associate Minister of Health Ayesha Verrall has slammed Bay of Plenty District Health Board (DHB) after it asked Pacific people to show their passports at Covid-19 vaccination appointments.

The DHB apologised last night over the move, acknowledging it was not the DHB's policy, nor a requirement, and that it had affected trust and confidence with its Pacific communities.