Northland will move to level 3 tonight after a woman used false information to obtain travel documents and spent several days in the region.

Covid-19 Response Minister Chris Hipkins said the confirmed case travelled from Auckland to Northland and had been to several places, warranting the change.

And it's believed she was travelling with another woman who authorities have yet to locate.

A reporter at a hastily arranged press conference said they had been told the woman is a sex worker but Hipkins said he could not confirm that - he had not been briefed that was the case.

He said he was incredibly disappointed at the events which have led to Northland being placed into level 3.

"Updated information provided by the police today shows the case moved extensively around Northland after travelling there on October 2," Hipkins said.

"We recognise that it is unusual to put a region into alert level 3 when there are no further cases. However, it's vitally important that we get ahead of any potential spread, and set up widespread testing and continue contact tracing efforts."

Restrictions will remain in place until 11.59pm on Tuesday and will be reviewed at the Cabinet meeting on Monday.

It will be the same level 3 as applies in the Waikato. The easing steps announced for Auckland earlier this week will not apply to Northland.

"The Auckland boundary will stay in place," Hipkins said.

"A public health investigation continues to identify close contacts and any potential locations of interest."

Northland mayors have expressed anger and frustration that one or two people have potentially brought the virus to the region.

Whangarei mayor Sheryl Mai said another change in alert level was "unacceptable" and that it would hurt businesses and holidaymakers that have flown from other parts of New Zealand during the school holidays.

Far North mayor John Carter said Northland going back up to level 3 was "unfortunate and frustrating" and urged everyone to get vaccinated if lockdowns were to be minimised or prevented.

The woman who's tested positive was in Northland from the afternoon of October 2 until the evening of October 6.

She is believed to have travelled around the region, including in Whangārei, Kamo, Paihia and Kawakawa, before returning to Auckland.

Testing centres operating in the Northland region are at Kaitāia Hospital; 1 Sammaree Place in Kerikeri, Dargaville Hospital; 20 Winger Cres in Kamo; and Pohe Island in Whangārei.

"Widespread testing and wastewater testing will take place over the weekend," Hipkins said.

"Every Northlander needs to stay home, get tested as soon as possible if they have symptoms, and continue to check the Ministry of Health website for updated locations of interest. And of course vaccination centres continue to be open in alert level 3.

"We know many people in Northland live rurally, but the advice is the same for everyone – get vaccinated, get tested, and follow the alert level 3 requirements.

"As we have seen in Waikato the virus is finding its way into rural areas and finding unvaccinated people. Distance is no barrier. It's never been more urgent to get vaccinated and we urge everyone to act now."

Hipkins said the decision followed an emergency meeting of ministers this evening.

He confirmed that the case had not been co-operating with contact tracers, and there was some information to suggest she was not travelling alone.

He said it had been difficult to find the case too, after the first weak positive test result, and it took police involvement to find her again.

He said there was no information at this stage to say whether the case was involved with a gang, or connected to a gang.

At this point, he said the case had obtained a travel document by providing false information - though he said this information was yet to be confirmed.

He couldn't say why the woman had travelled, but the document had permitted the travel under the "social services category".

He said he didn't know at this stage how many contacts there might be connected to the case.

The person the woman travelled with has now been identified but remains at large. Hipkins said he didn't know where she was.

Both the case and her contact were women, he said.

He couldn't say whether she was reluctant to be co-operative because she might be trying to protect anyone else from being contacted by police.

The virus reaching those harder-to-reach places made contact tracing more challenging, he said.

"This has been the starkest of those."

Hipkins said vaccination rates in Northland are low, which was also a factor in the decision to move Northland to level 3.

About 70 per cent of the eligible population there have had one dose, while 48 per cent have had two doses. Those rates are lower for Māori: 52 per cent for one dose and 32 per cent fully vaccinated.

There was a chance that the virus could spread through the region quickly, Hipkins said.

The virus had a way of finding the unvaccinated, he said, and he urged people in Northland to get the jab to protect themselves and their loved ones.

The first locations of interest for Northland were added to the Ministry of Health's website on Friday night.

They are the BP Connect Wylies petrol station at 49 Maunu Rd, Woodhill, Whangārei, from 11.20pm on Friday October 2 to 12.20am October 3, and the Z Kensington service station, corner of Kamo Rd and Nixon St, Whangārei, from 3.45pm-4.45pm on October 4.

At 1pm today, it was confirmed 44 cases were in the community, 12 of which were unlinked.

Forty-one were in Auckland while three were in the Waikato.

"We acknowledge today's numbers are higher than recent days," director of public health Dr Caroline McElnay said.

"This is not unexpected because there have been a number of contacts of new cases and we can expect to get fluctuations from day to day."

At 1pm, there were 26 unlinked cases in the past fortnight.

Today extra regions in the Waikato awoke to an expanded level boundary, after new cases popped up outside the initial boundary on Wednesday.

The level 3 settings in the Waikato do not include the easier restrictions Aucklanders have enjoyed since Wednesday, which include outdoor socialising of up to 10 people and two households.