New Zealand is heading into the middle of winter, Covid-19 case numbers are rising, and health professionals warn it could mean a return to red restrictions.

However, there are other cards that could be played to help push back the Omicron winter bite.

There was a jump in cases that started late last month: 8638 cases were reported on June 25 and 8028 on June 28, both days being more than 2000 cases more than the day before.

Daily reported cases have only dipped below 5000 once since then, which was on Sunday, and it is known that new case numbers typically dip on weekends.

Monday's 6498 cases kept with the trend.

The week wound up with a seven-day rolling average at 7046 - last Monday that figure was significantly lower, at 5132.

University of Auckland infectious disease expert Dr Siouxsie Wiles says another wave has been expected and should not come as a surprise.

Officials, including Prime Minister Jacinda Ardern, have pointed to it multiple times throughout the year.

On February 21, 2022, she talked about how New Zealand would "go through our first winter with Covid at the same time that flu returns, following two winters of very low rates ... we approach winter with the potential of more illness".

Then on April 4, 2022, Ardern spoke of the need to let the health system "recover and be ready for the expected winter surge".

Wiles says rising case numbers can be seen around the world, as immunity wanes and new variants emerge.

She says people should not feel invincible if they have previously had Covid-19, because they can get re-infected.

And she issued a reminder that while people might be tired of the pandemic, that does not mean it no longer exists.

"Ignoring something doesn't make it go away. It just means that you're less prepared and will respond worse when it does actually happen."

But there is still time to "start putting in place all of the things that will help keep those numbers lower", Wiles says.

Whilst that includes a possible return to red traffic light restrictions, Wiles says there are also other tools "we could be doing right now, that we aren't doing very well", to keep Covid-19 at bay.

"So everybody wearing masks in as many situations as they possibly can ... opening doors and windows, you know - looking into improving ventilation."

People getting up to date with their Covid-19 vaccine doses - getting their second if they had not got around to it, or their fourth dose if they are eligible will also "really, really help", she says.

And help to reduce the amount of illness in the community is what some sectors desperately need.

Recruitment firm Hays' managing director Adam Shapley says rising cases are "bad news" and will slow productivity.

"There's more people off sick than I've ever seen in 20 years of work," he said.

Most businesses are trying to get by with the staff they have, focusing on long-term hires instead of filling short-term gaps, he says.

"But as it stands, today, there's already a shortage of people in the workforce.

"So most organisations are probably running at a highest need for staff than they have been for many years, and this has just added a further complication in to what is already a challenging situation."

With the rise in cases, the Ministry of Health is warning people to respect the rules if they are at a hospital.

It notes there was an increase in the number of Covid-19 positive inpatients in the Waitematā DHB, as well as evidence of visitors passing Covid-19 on to patients at North Shore Hospital.

-RNZ/Jake McKee.