There is one new case of Covid-19 in managed isolation today.
The Ministry of Health said three cases were also being investigated as historical infections.
"The total number of active cases in New Zealand today is 28."
Today's update comes as authorities in Australia announce restrictions for the Greater Sydney areaafter a man in his 50s in the community tested positive for the virus yesterday - despite having no links to the border.
The man's wife has also tested positive for the virus today.
New South Wales Premier Gladys Berejiklian announced today masks are compulsory in indoor venues and no gatherings larger than 20 people are allowed in residential homes for the next three days.
Chief health officer Dr Kerry Chant said that while ten close contacts of the man who tested positive yesterday have been identified, the "missing link" in the case is still out there.
Genomic testing shows the sequence from the new case in the community, an Indian variant, matched with an overseas case, who had travelled from the US and returned to Australia on April 28.
"We can't find any direct link between our case, so what we're concerned about is there is another person that is as yet unidentified that infected our case," Chant said.
New Zealand officials say they remain in contact with their Australian counterparts on the case.
"Anyone in New Zealand who has been at any of the locations of interest at the specified times should contact Healthline on 0800 358 5453, self-isolate and be tested as soon as possible," the ministry said.
The locations of interest can be found at the NSW Government Health website.
"Individuals in Australia who were at a location of interest at the specified times should follow New South Wales health advice regarding isolation and testing, and should not travel to New Zealand. The ministry has requested airlines communicate this message to anyone before flying to New Zealand from New South Wales."
The public health assessment of the risk remained low, the ministry said.
"We expect to be able to provide a further update on the situation in Sydney later today."
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Thirty-two people in New Zealand have been advised to isolate at home until they receive a negative result from a day 5 test.
So far 22 people have returned a negative result.
Three new cases were identified in New Zealand yesterday - all of them in managed isolation facilities in Auckland.
They include a person who arrived from the US on Monday and tested positive for Covid-19 on the first day.
The second case is a returnee from the United Arab Emirates on April 30 and who tested positive for the virus on their day 3 test.
The third person is another traveller from the UAE who touched down on April 20. They tested positive on the first day of testing.
Five people who tested positive to Covid previously had since recovered, officials said.
And as of yesterday, the total number of active cases was 25. The total number of confirmed cases in New Zealand is at 2273.
Since the first day of this year, there have been 53 historical cases of Covid out of a total of 457 cases.
Because of the new positive Covid case in Sydney, there were concerns that they may pause quarantine-free travel between Sydney and New Zealand or other parts of Australia.
Kiwi health officials are continuing to monitor the Sydney case but say the risk is now and they do not recommend any change in quarantine travel between New Zealand and Australia.
Sydney risk 'low'
The Ministry of Health said their assessment of it being a public health risk to New Zealand was low.
"On that basis, the ministry does not - at this stage - recommend any change in quarantine-free travel between New Zealand and Australia."