Jacinda Ardern says a community case of Covid 19 in Christchurch shows why New Zealand needs to continue taking a cautious approach.

A person working in the Sudima Hotel at Christchurch Airport, which is a Managed Isolation Facility, has tested positive for Covid 19.

The Prime Minister says the case shows why we need a rigorous quarantine system.

"We've built the system to be able to deal with that. It's going to happen from time to time, but we have to make sure that we have a very rigorous regime so that when that happens, we're managing it properly."

She told Mike Hosking that means limiting the number of essential workers and others coming into the country, to a manageable number.

"We want to be able to bring in more essential workers, but what I'm mindful of is while we look to grow capacity, we have to make sure we're doing it safely."

Covid-19 will be a top priority for the Government, which will be officially sworn in on Friday. 

The Prime Minister has announced a new Cabinet line-up, saying Labour has a mandate to govern.

She's named Grant Robertson as her deputy, Chris Hipkins has a new Covid-19 Response Portfolio, and Nanaia Mahuta is the first Maori woman Foreign Affairs Minister.

However, Ardern says a higher than usual number of special votes are delaying the final election count.

She says the Electoral Commission asked for an extra week to count the votes, because of forecast higher numbers of special votes.

"Some of the changes that were made, for instance to allow people to enrol and vote on the same day, increased the number of specials." 

Despite this, Ardern is pleased with the speed with which her administration is taking shape.

The Prime Minister told Mike Hosking that, relative to every formation of Government, she's been moving faster.

"We'll be swearing in the Government before we even have the special votes all counted, which is a substantial number this time, because we still feel that we've got the mandate."