COVID-19: New Zealand could see between 50 to 120 more cases of Delta - Bloomfield

New Zealand can expect to see between 50 to 120 new cases of COVID-19, thanks to the high transmissibility of the Delta variant.

Director-General of Health Dr Ashley Bloomfield said on Wednesday modelling suggests these numbers are entirely possible.

"We had some modelling done which uses a large range of assumptions, hence the range there...broadly speaking, two different modelling exercises have suggested picking up a case like this there could be between 50 to 120  [more cases] to give people an idea of scale."

He says the best way to protect Aotearoa is for people to "sit tight and stay in their bubbles".

On Wednesday, New Zealand recorded another six new cases of COVID-19 - all linked to the original case, a 58-year-old Devonport man.

All seven cases have contracted the highly transmissible Delta variant, with one person working at Avondale College and the other at Auckland Hospital, creating a significant risk.

Prime Minister Jacinda Ardern says she is expecting more cases.

"But the best place to be when expecting further cases is the highest alert level possible...we're finding these cases and finding them in good time but we are now moving to locations of interest which are much larger."

She says the risk is that people who were in the locations of interest will no longer be able to be identified by interviewing infected people.

"They'll be alongside strangers, so we need people to identify themselves if they have been at the locations of interest."

As the people infected are in their 20s, Ardern says it's expected cases will rise.

"The age group and demographic means they are more likely to frequent environments where they were exposed to others."

The two new cases are a 21-year-old woman and 19-year-old man who are friends and spent time with the existing cases. 

One went to a church on the North Shore on Sunday morning. They both also went to a nightclub in central Auckland on Sunday night.

The four other cases announced earlier on Wednesday are a work colleague of Case A, a 20-year-old male, and three flatmates - the fully vaccinated nurse, 21, a teacher at Avondale College, 25, and a male, 29.

The seven cases are all linked.

The wife of Case A, who is vaccinated, has returned a second negative test.