The Wellington region, including the Wairarapa and Kapiti Coast, have been put into alert level two until Sunday.
It comes after a man from Sydney travelled to Wellington over the weekend, and tested positive for the virus on their return to Australia yesterday.
Under level two, gatherings are limited to 100 people, masks are mandatory on public transport and social distancing is required.
Schools and ECE centres will stay open, hospitality venues can open but need to apply the three S's - seated, separate and having a single server.
Covid-19 response minister Chris Hipkins told Heather du Plessis-Allan says the risk is low - but there's not no risk.
"We know that we've got a couple of exposure events where we have someone with Covid-19 in an environment where Covid-19 could potentially spread reasonably quickly."
The Government has faced criticism for not alerting the public earlier to the case, with Hipkins and Bloomfield telling media today they first learnt of the case between 7 and 8:30pm on Tuesday night - but did not publicly flag the case until 6am Wednesday morning.
The Minister says it is "not a fair categorisation" of the situation.
"When we do get information about a case, we do have to gather information about the exposure.
"For example if someone was in Wellington, had subsequently left and had been positive for Covid-19 after they left wouldn't necessarily trigger the sort of response we've had. It was the nature of the exposure event, and it takes a little while to assemble that information."
While the trans-Tasman bubble has given him "some sleepless nights", Hipkins has