She said at this stage there were no signs of community transmission and no known link to MIQ yet.
The New Zealand Ministry of Health said it would remain in close contact with its Australian counterparts with another update expected today based on further testing results and health assessment.
"Anyone planning to travel to New South Wales should take into account that advice from health authorities could change at any time, and be prepared for their travel plans to be disrupted."
In Sydney, genome sequencing is underway and results are expected in the next 24 hours to establish whether there's any link to any recent returnees.
The man, who lives in the eastern suburbs of Sydney, was an active user of Australia's QR code app and a number of locations of interest have been identified.
The man in his 50s was "very active" in the inner east of Sydney, visiting popular sites such as Bondi Junction.
Overall NSW currently has 108 Covid-19 cases, however, this recent positive case will be included in Thursday's numbers.
Earlier on Wednesday, New Zealand health officials announced there were three new Covid cases in MIQ to report - two from the United Arab Emirates and one from the United States.
The ministry also revealed that 32 people in New Zealand have been advised to isolate at home until they receive a negative result from a day 5 test, as a result of the Brisbane Airport green zone breach.
To date, three passengers caught up in the breach have returned a negative result.
"Remaining passengers who weren't at the locations of interest at the specified times should continue monitoring their health and, if symptoms develop, call Healthline and get a test," the ministry said.
"The risk from this event continues to be assessed as low."
Health officials also updated vaccine numbers.
A total of 304,900 doses have now been administered - 87,297 people have received both doses, while 217,603 people have had their first jab.
According to the Ministry of Health's plan, NZ's vaccine rollout is at 103 per cent. That means it's just ahead of schedule.
But the breakdown differs across regions around the country. The MidCentral district health board area, for example, is at 150 per cent. Northland is at just 70 per cent.
In terms of the areas where the most vaccines have been administered, Counties Manukau is at the front of the pack with 29,410 total jabs so far.
Of those, 13,664 people have had their second dose.
