The Covid-19 Response Minister Chris Hipkins says the Ministry of Social Development approved - and then revoked - the border exemption of two women who went to Northland from Auckland.
Both have since tested positive for Covid-19.
Hipkins told Morning Report the pair had crossed the border before the exemption was revoked.
"There was a degree of error in the approval in the first place, and that was corrected, but obviously it was corrected after they had already travelled across the border."
He could not confirm rumours about whether one of the women was hiding in the car when crossing the border, and said it would be up to police to decide whether to search a vehicle, although doing everyone would take a lot of time.
"Given the volume of people who are having to travel in the queues that are already forming, they [police] will be relatively efficient in the way they process those queues, and so they may not be doing a thorough inspection of every vehicle."
He said one of the two women involved is now providing information to help identify locations of interest.
"We now have the second person involved here, is cooperating and is providing information on locations of interests and the nature of the activities undertaken, whilst in Northland.
"That certainly helps us to identify the risk, isolate the risk, and that increases the chances of Northland being able to come back down the alert levels."
