On Wednesday night, the health ministry announced two people had returned positive results after previously testing negative twice and completing their mandatory isolation.

"It is yet to be confirmed if they are recent or historic infections. Further urgent testing is being carried out this evening," they said in a statement.

"The two people are asymptomatic and ... both individuals are currently self-isolating at home."

The tests heighten fears that a recent community case, a 56-year-old Northland woman announced on Sunday, might develop into an outbreak or require the return of restrictions.

The Australian government responded to the news by delaying a decision on whether to re-start quarantine-free travel from New Zealand.

Australia put a 72-hour ban on free passage for travellers from Aotearoa after learning of the new community case.

Importantly, there is still no evidence of community transmission of the deadly virus.

Officials believe the woman caught the virus during her stay at Auckland's Pullman Hotel.

The cases prompted wide re-testing of other recently released returnees and staff members.

Three days of testing - including 16 of the woman's close contacts and hundreds of others - failed to unearth a positive result until late on Wednesday.

New Zealand's director general of health, Ashley Bloomfield, said those negative results were "encouraging signs" but "the situation is evolving and we're not breathing out just yet".

The scare has also prompted New Zealanders into improving their personal contact tracing efforts.

Kiwis logged more than one million check-ins using the government's COVID Tracer app on Tuesday.

Australian Associated Press