Concern about how quickly Delta could spread around the country.
Cases have been reported in Karāpiro and Kāwhia - well south of the Level Three border -- and a weak positive has been reported in Whangārei.
One mayor is now calling for the entire upper North Island to be put back in Level Three -- while Wellington Mayor Andy Foster says it's only a matter of time until Covid spreads much further south.
Auckland University epidemiologist Rod Jackson told Mike Yardley the Delta variant is proving very difficult to control.
"Delta is like a human flamethrower in a forest; if you're vaccinated you're like a clean, green pine tree. If you're unvaccinated you're like an Aussie gumtree."