All of New Zealand south of Auckland will move to alert level three at midnight Tuesday, but Auckland is likely to stay at level 4 for two weeks, the prime minister has confirmed.

These settings will be reviewed a week later. Auckland and Northland will remain at level 4, with decisions on that to be considered on Monday.

Jacinda Ardern and director-general of health Ashley Bloomfield have spoken about Cabinet's decision to change the country's lockdown status.

Ardern said today's decisions will "put us in the best possible position to give as much certainty as we can".

She said it was likely at this stage Auckland will remain at level 4 for a further two weeks.

"We will need to be confident we've stamped it out and have cases contained and isolated."

She said Northland was being included because of a recent case in Warkworth and the government was concerned about northbound journeys, but Northland is unlikely to be kept in the same position as Auckland in the long term.

She said one of the exposure sites in Warkworth, while closed to the public, was a relatively large workplace.

Ardern said we "may be seeing the beginning of a plateau of cases" based on the case numbers today.

"But caution is still required."

She said it was clear from the outbreak that Delta was more infectious and moved more quickly.

"Of the cases reported yesterday, roughly half were household contacts. Unfortunately we know from Australia that household members are almost universally becoming infected with Covid-19, that means you can expect our numbers to continue for some time as household contacts continue to test positive."

She said public health units were observing very fast infection times with Delta, but it did not change the fact the strategy right now was elimination and "every New Zealander can play their part in that".

Of the new cases reported yesterday, only 10 had any new exposure events, "and some of these were pre-lockdown". She said compliance was very high.

"Lockdown is making a difference," she said.

"We know Covid's not going away quickly, but out strategy can evolve."

Ardern said previously levels 4 and 3 have been used to reduce spread, now level 4 was being used to do the bulk of the heavy lifting.

The alert level for districts outside Auckland was due to expire tonight, but the prime minister said there were two reasons the rest of the country is being kept at level 4 for three extra days.

The first is the confidence of an almost 14-day cycle since cases were discovered, the second is because of the cases in Wellington.

"We also have those contacts in the south and that full two-week transmission cycle is very very helpful in terms of our confidence."

There is also the wastewater result in Christchurch, and further tests will give more confidence over that, she says.

She has given a reminder of the rules, which can be found here.

She said checkpoints will be in place, and no one will be able to move between alert levels without an exemption. Police have been working to make sure the boundaries work as smoothly as possible, she says.

Employers that will be affected should seek an exemption.

"If you are not an essential worker, you are not able to cross the boundary."

Today, the Ministry of Health revealed there were 70 new cases of Covid-19 in the community.

In a statement, the Ministry of Health said there were 19 community cases in hospital, including one in ICU. All were in a stable condition.

The total number of cases linked to the current community outbreak was 347 - 333 in Auckland and 14 in Wellington, the ministry said.

Director-General of Health Dr Ashley Bloomfield and Prime Minister Jacinda Ardern. Photo: Stuff / Robert Kitchin