The breaches occurred on the same floor of the hotel on Sunday according to RNZ.
The joint head of managed isolation and quarantine Brigadier Rose King said in a statement that their stay will be extended should anyone test positive.
All 12 involved are now in isolation and all are undergoing further tests, and none has tested positive to date.
The returnees arrived on 11 June from Samoa and were not RSE workers.
They did not require day 0/1 tests, given the country of origin, and all day 3 results came back negative.
