QR app codes are now mandatory for businesses and services, Prime Minister Jacinda Ardern and Director-General of Health Ashley Bloomfield have revealed, as they announce new Covid-19 cases in New Zealand.

Dr Bloomfield says there is just one new confirmed case in managed isolation recorded today, plus the four cases of community transmission announced last night.

Four further probable cases have also been identified, he says, and they are all in isolation.

There are 22 active cases in New Zealand, he says.

Ardern and Dr Bloomfield announced increased Covid-19 alert levels across the country last night after four new cases of community transmission.

Those four were members of a family, and Dr Bloomfield revealed this morning that one of them had travelled to Rotorua while symptomatic.

This afternoon he said the visit to Rotorua had not resulted in a positive test for any of the close contacts of the positive case and her child.

He says the symptomatic family members visited Waiora Lakeside Hotel, the Skyline Gondola and Heritage Farm and 3D Gallery.

Two of the new probable cases are also family of the first case, and two are co-workers of the family, Dr Bloomfield says. Three are adults and one is a teenager, all of them symptomatic.

Over 200 close contacts of the family had been identified by about midday, Dr Bloomfield said.

He said any employees or visitors to Americold in Mt Wellington, and Finance Now on Dominion Road - and their households - should remain at home in isolation.

Across the world, there have been 19.9 million cases yesterday, Ardern says. New Zealand's approach has been successful, but it takes us all working together.

"We know how to beat this, but we also know we don't need to look far to see what it can mean if we don't get on top of it. We have a plan and now is the time to follow it."

App QR code display to be mandatory - Ardern

Ardern said that at midday today a new public health order also came into effect.

The order provides the legal basis to require people to stay at home, unless they are working in places where it is safe for them to do so.

It also includes two new provisions. It is now mandatory for any business or service to display the QR code for the tracing app at all entry points. Businesses will have one week to comply.

People travelling out of Auckland are also required to wear a mask while on a plane.

The Auckland region moved to level 3 at midday today, with the rest of New Zealand moving to level 2 simultaneously. The increased levels will remain for three days until midnight Friday, when alert levels will be reassessed.

Ardern said the Covid-19 leave support scheme was there for all businesses experiencing financial hardship, and applications for the wage subsidy extension would remain open until 1 September.

The small business cash flow scheme remains open until 1 December and the Covid relief payment for people made redundant remains open until 13 November.

Finance Minister Grant Robertson and Treasury are working on targeted economic support for Auckland if the city is to remain in level 3 beyond Friday, Ardern said.

"With support aside, the best economic response remains that strong health response, going hard and going early with a lockdown is still the best strategy for getting business back open as soon as it is safe."

Level 3 travel measures also include roadblocks being set up by police and defence force at the exits from Auckland.

Rest homes are also going into full lockdown until midnight on Friday, effectively operating at level 4.

The Ministry has begun a mass testing regime, calling for anyone with symptoms to seek testing. Auckland's Covid-19 testing centres are extremely busy, with queues snaking kilometres as hundreds of people line up for tests. The healthline has been inundated with calls as well, with reports of some people waiting on hold for hours.