Director-General of Health Dr Ashley Bloomfield says the "extra few days" at Level 2 should give those in the South Island confidence that the risk of a case being exported from Auckland is as low as possible.
The Government announced yesterday that the country will remain at Level 2 at least until midnight on Monday next week, at which point the country apart from from Auckland is set to drop to Level 1. Auckland's alert level setting will also be considered then.
Prime Minister Jacinda Ardern said those changes were contingent on case numbers "tracking as they are".
She said current modeling suggests there is still a chance of a case being spread from Auckland to another part of the country, and the Government wants to lower that risk even further before the alert levels are dropped.
"It only requires one person travelling and attending a super-spreader event somewhere else in the country and we could be looking at further restrictions elsewhere," Ardern said.
Speaking this morning to TVNZ1's Breakfast, Bloomfield said the delay of moving the rest of the country to Level 1 should give people outside Auckland confidence.
"We are confident the cluster is contained - and as the Deputy Prime Minster [Winston Peters] said, indeed there is a low risk of cases outside of Auckland - but there's not no risk," he said.
"At the moment the modeling is showing there's still a 30-40 per cent chance of a case outside of Auckland being seeded from someone travelling out of Auckland, and around a 10-20 per cent likelihood in the South Island.
"There is a lower risk in the South Island, but it's not no risk, and these extra few days will just help reduce that risk even further.
"It will have given us a couple of weeks just to detect if any cases have been seeded outside of Auckland, and particularly the South Island.
"Our contact tracing has happened very quickly, which is good. We've been able to get people isolated and tested very quickly - those who are close contacts.
"We've also extended those out to, as we call, contacts of contacts, just to be doubly sure.
"We've used that through the outbreak and that's what we're continuing to do, which is part of our plan to move down through the alert levels as quickly as possible.
"But the advice yesterday was that we don't think its time to do that quite yet."
Ardern said on Breakfast this morning that the Government continues to take a cautious approach to alert level changes.
"Many people believe that the rest of the country should have been at Level 1 - our view is that, no, we needed to take a cautionary approach, which is what we've done."