There's a very low risk of undetected community transmission of COVID-19 in New Zealand, according to Dr Ashley Bloomfield.
But during a press conference on Wednesday afternoon, the Director-General of Health couldn't "categorically" rule community transmission out.
"What I can say is that there is a very low risk in the first instance because of the circumstances - indeed the 14 days [in quarantine] - but also the wide testing we are doing; 45,000 tests since the 16th [of June]," he explained.
That level of testing was reassuring the Ministry of Health there's no undetected community transmission, Dr Bloomfield told reporters.
His comments come after it was revealed 51 out of 55 people who left quarantine early were not tested for coronavirus before their release.
Dr Bloomfield said the ministry's job was to detect COVID-19 should it be in the community.
Aircrew, quarantine and isolation facility staff, shuttle drivers, cleaners, and border staff must also now undergo consistent and mandatory testing for COVID-19.
"We've got these high numbers of tests being done and we have our surveillance testing that is also coming on stream as well around the border," Dr Bloomfield said.
Since last week's border botch-up, where two women were let out of quarantine on compassionate grounds without tests and later confirmed to be infected with COVID-19, the Government has ordered the further strengthening of the border including making it compulsory to return a negative coronavirus test before leaving managed isolation. Everyone in managed isolation is tested on days three and 12 of their stay.
On Wednesday, ACT leader David Seymour labelled New Zealand's borders as the "world's dumbest".
"We are so far from smart borders that anyone who needs openness just took a massive setback," Seymour said.
During Wednesday's Ministry of Health press conference, Dr Bloomfield also revealed there is one new case of COVID-19 in New Zealand - a woman in her 60s in managed isolation.
She returned to New Zealand from India on June 18 and was in managed isolation at the Pullman Hotel. She has since been moved to Auckland's Jet Park Hotel, which is operating as a quarantine facility.