On Saturday night, a small number of ministers met and suspended quarantine-free travel with Australia, a move later attributed to fears around the case at a Northern Territory mine site.

Officials have since been manually checking arrivals to New Zealand against staff lists at the mine site to see whether fly-in fly-out workers have landed in Aotearoa.

On Monday afternoon (NZST), the Ministry of Health announced two of around 900 workers had travelled to New Zealand.

Both are isolating. One has returned a negative test; the other's result is expected on Tuesday.

The trans-Tasman bubble was created on April 21 when New Zealand removed its quarantine requirements to Australia.

Since then, it has suspended travel to NSW, Western Australia and Victoria temporarily in response to outbreaks.

Saturday's suspension is the first whole-of-country shutdown, and runs contrary to its public plan on how it would manage the border.

While there is no prospect of re-opening to NSW as it contends with its major Bondi cluster, Ms Ardern said a reassessment would take place early this week.

"As we assess ... you may see different guidance for different states," she told TVNZ.

The border to NSW will stay closed until July 7 at the earliest.

New Zealand is on a 120-day streak without community transmission but Wellington is currently on high alert for new cases after an infected Sydney man visited the capital.

The government have placed more than 2000 residents into isolation after categorising them as close contacts.

Mass testing has failed to show up any local cases since.

Ms Ardern said the man's wife, who also travelled to NZ, had also tested positive on return, suggesting Wellington wasn't yet out of the woods.

"I will always maintain a very cautious approach all the way through," Ms Ardern told TV3.

Australian Associated Press