An Air New Zealand flight from the Covid-19 free Cook Islands has been named as a location of interest.
Flight NZ945 from Rarotonga arrived in Auckland at 5.30pm on Tuesday this week.
Passengers seated in rows 53 to 57 - indicating the infected person may not have been a crew member - were considered close contacts.
They should self-isolate, get tested immediately and again on day five after exposure, the Ministry of Health said.
"Further isolation and testing requirements will be provided by Public Health."
There have been no community cases of Covid-19 in the Cook Islands, which has a double-dosed vaccination rate of 96 per cent of the eligible population.
Seventy per cent of those eligible have also received their booster.
A spokeswoman from the Cook Islands' Ministry of Health told Newstalk ZB she wasn't aware the flight was a location of interest, so didn't have any details on whether the infection originated in the island chain or in New Zealand.
She was trying to find out more late on Saturday night.
The Cook Islands only opened to quarantine-free travel with New Zealand days before transmission of the highly infectious variant was detected in the New Zealand community last month.
The country's government decided to keep the existing quarantine-free border with New Zealand open, albeit with extra Covid-19 prevention measures in place.
Travellers must have received their second vaccination at least 14 days before departure and have evidence of a negative Covid-19 test before departure to be eligible for quarantine-free travel.