Two Covid-infected women who put Te Tai Tokerau into a 12-day lockdown and hid from police, won't be charged.

They were so uncooperative, investigators were forced to rely on CCTV footage to trace the Aucklanders' movements to hotels, petrol stations, shops and a campsite last October.

Prime Minister Jacinda Ardern called their actions "irresponsible," "dangerous" and "extraordinarily frustrating".

Whangārei Mayor Sheryl Mai was "ropeable" the region had to go from level 2 to 3.

One of the women spent days evading police, before she was taken into custody.

Both were forced into MIQ.

The Ministry of Social Development https://www.rnz.co.nz/national/programmes/morningreport/audio/2018816152/covid-19-ministry-of-social-development-approved-border-crossing-for-northland-case-hipkins mistakenly approved business travel documents] allowing the pair to enter Northland from Auckland's Delta lockdown.

They were later revoked.

RNZ can reveal police finished "a thorough investigation which was also the subject of a legal review," last month.

They concluded, "there was insufficient evidence to prove that the women obtained their business travel documents by deception or that they crossed the alert level border for a purpose other than what was stated on those travel documents".

They said there was "insufficient evidence" to prosecute.

No Northland cases were connected to the women.