A Covid expert says he is not ruling out New Zealand going back into red within the next few weeks as Covid numbers continue to rise.

There are 9629 new community cases of Covid-19 in New Zealand today - up by more than 3000 from yesterday.

The regions with the most new cases in the past 24 hours are Canterbury, with 1549 cases, and Waitematā, with 1266.

Auckland recorded 924 cases, Capital and Coast had 827, Southern 809 and Counties Manukau 731 new infections.

Dr David Welch, senior lecturer at the University of Auckland's Centre for Computational Evolution and School of Computer Science. Photo / Jed Bradley

The worst-affected region remains Auckland, with 15,983 people infected with Covid.

University of Auckland senior lecturer in computational evolution Dr David Welch has been mapping the emergence of the BA.5 Omicron subvariant and its contribution to the rise in Covid numbers.

"Going back to red is something that the Government would be looking at very closely right now, they'd be looking at how the hospitals are coping and what are the projections," Welch said.

"Our hospitals are already really, really full. Not only because of Covid but also because of other winter illnesses. We expect these cases to continue to rise and there'll be just more pressure on the health system."

Prime Minister Jacinda Ardern said the rise in case numbers was "no expectation" of moving to red.

Last week, Covid-19 Response Minister Ayesha Verrall said: "When we moved out of red in April the rolling average of cases was nearly 10,000 a day and there were over 500 people in hospital including 28 in ICU".

The Ministry of Health today also reported a further 24 Covid-related deaths. Of the 24 deaths, three people were in their 40s, five were in their 70s, seven in their 80s, and nine were aged over 90.

There are 493 people in hospital with the virus, including 11 in intensive care.

And the Omicron subvariant BA.2.75 has been detected in New Zealand for the first time.

Welch said it was the BA.5 Omicron subvariant that "we should be worried about".

It is appearing as more transmissible and will overtake BA.2 to be the dominant variant in a matter of weeks, he said.

"It's now gotten close to the point where BA.5 is becoming the dominant variant, and so that's why we are seeing the case numbers going up," he said.

"The BA.2.75 is yet another variant, and one that we're watching closely and it's just kind of come to the attention of people around the world. In terms of what's happening here, it won't be having an impact on case numbers right now."

The ministry says at this stage, there is no evidence BA.2.75 requires a shift in the public health settings already in place to manage other Omicron variants.

On Friday afternoon, analysis of whole genome sequencing confirmed two cases in New Zealand with BA.2.75. Before testing positive for Covid-19, both had recently travelled from India.

BA.2.75 is a recently identified second-generation subvariant of BA.2, the dominant variant circulating in New Zealand at this stage. BA.2.75 has only been recently identified as distinct from BA.2, and evidence on its transmissibility, immune evasiveness and severity is still preliminary and emerging.

"I certainly won't rule out going back into red within the next few weeks, but then again I'm not sure if it is politically feasible and whether people will listen this time," Welch said.

"But there are a lot of things that people can do without having to wait for the Government to make it mandatory, like mask-wearing at schools, for example. Anecdotally, schools that have made masking mandatory have not had the illnesses that other schools have."

Red is the most restrictive traffic light setting, where face coverings are mandatory when travelling on public transport, in retail and to an extent in education. Public facilities and retail outlets are open, with capacity limits.

Welch said everyone who is eligible for boosters should be taking them - especially those who can now get the fourth vaccination jab.

"People need to reset and recalibrate their risk level. We have been so used to going out and about a bit more, and that was fine when case numbers were lower and decreasing," Welch said.

"Now we're in a situation where they are higher and increasing and people should reconsider when they should be getting into that crowded environment, and when they should be wearing that mask or not."