Representatives from manufacturing, food and grocery, and healthcare are all warning of serious shortages if the self-isolation period for close contacts of Covid-19 cases is not reduced.

The government has estimated 350,000 people at once could be self-isolating during this outbreak.

At present a person deemed a close contact of a Covid-19 case must isolate for 10 days, and a household contact is required to isolate for 24 days, even if they do not return a single positive test.

Food and Grocery Council chief executive Katherine Rich says it will be difficult for the sector to keep supermarket shelves stocked if isolation periods were not reduced.

"[The government] must address the stand-down periods, otherwise we're not going to have enough people to be able to keep the whole food and grocery sector functioning."

She says if the definition of a close contact is not eased, entire shifts of factory and manufacturing staff are going to be sent home for days at a time if there is a case in the workplace.

That could cause a critical shortage of staff and jeopardise a company's ability to produce food at all.

"That's when the community starts to get very anxious. They can understand the odd empty shelf, but when you get shelf after shelf empty, current citizens have never experienced that kind of shortage."

Rich wants New Zealand to follow Australia where some close contacts could go to work providing they test negative and are asymptomatic.

"For critical food and grocery workers, they have given the industry an exemption, so if you return a negative test you can go back to work, and you keep tracking it up until the point there is a change."

Rich says the entire sector is operating with good PPE, high quality masks, and are socially distanced, so a positive case is a lower risk than one in the community.

The government has signalled it will reduce isolation requirements when the outbreak is recording more than 1000 cases a day, at stage three of the Omicron response, but not until then.

Auckland GP Peter Boot expects staff shortages will be so dire in healthcare that some doctors and nurses will have to work while they are infected with Omicron.

"That is what has happened elsewhere, and I expect it will happen here," Dr Boot, medical director of Northcare Accident and Medical on Auckland's North Shore, says.

He has upwards of 60 staff and is frantically trying to work out how they will continue to provide a good level of care when staff need to isolate.

It will be incredibly difficult for his clinic, and he did not expect people's compliance with isolation rules would last.

"I expect the government's system, where [cases] are meant to stay at home, and their families are meant to stay at home for longer, will be just disregarded by large sectors of society who have to work or just don't want to stay at home. I am sure the whole thing will fall to pieces quite quickly."

At Auckland Hospital, medical staff are told to be prepared to step in to do other roles if needed to fill gaps.

It's predicted up to 25 per cent of staff could be off due to sickness or isolation requirements when the outbreak takes off.

In a memo from senior management, staff were also told they may be cleared to return to work five days after testing positive for Covid-19 if necessary and their leave may be cancelled.

It is predicted up to 25 per cent of Auckland hospital staff could be off due to sickness or isolation requirements when the Omicron outbreak takes off. Photo: RNZ / Dan Cook.

The senior doctors' union, Association of Salaried Medical Specialists, says any doctors changing to work in another area will need supervision.

At the heart of the ability for people to safely work is testing and identifying cases.

The fastest way is a rapid antigen test (RAT) which is sensitive and can miss some cases, especially those early in their infection or who are asymptomatic.

The advantage is it returns a result in 15 minutes, meaning some workplaces test staff on arrival.

Employers and Manufacturers' Association chief executive Brett O'Riley says businesses are now unable to get their own rapid tests, after having to essentially convince the Ministry of Health they are worth using in the first place.

"We've been talking to rapid antigen test suppliers. We know that most of the stock that was previously in the country has now been taken up by the Ministry of Health. So businesses that have been previously using rapid antigen tests who are running out of stock can't get any access to stock," O'Riley says.

"In fact the Ministry of Health advised us to tell those businesses to start rationing. They advised us that last week, which is not satisfactory."

On Sunday during the announcement of the country's shift to the red traffic light setting, Prime Minister Jacinda Ardern said there would be a "test-to-work" programme that would apply to essential workers.

She says rapid antigen testing will be more widely and regularly available to essential workers, once case numbers were higher and contact tracing and isolation were having too heavy an impact on essential services.

More details would be given in the future, she says.

"What we'll be sharing a bit more detail on are those areas where people will be able to use rapid antigen tests on a regular basis to enable their workforce to stay in contact with work if they're a contact [of a case]."

O'Riley says businesses had managed to persevere through previous outbreaks.

"But this will be different. This is likely to have a much more profound impact than it has before, because for the first time we have some businesses who will be trying to open but not able to, because they simply can't get the workforce. That's the area of most concern to us."

Tomorrow, Ardern will give more detail on changes to the definition of a contact and self-isolation requirements, due to kick in once the country is recording thousands of cases a day.

On Sunday, Deputy Prime Minister Grant Robertson said they had been working "very hard" to avoid empty supermarket shelves and other goods shortages, and had been working with the sector and transport and logistics companies to "make sure" this would not happen.

Robertson says even a mid-level estimate of 25,000 cases a day would mean about 350,000 people self-isolating, both as cases and as contacts of cases.

"Obviously that's a significant number of people. Business continuity planning is something I know most businesses around New Zealand have been doing and they are working to see how they can manage their way through that.

There was a lot of work being done to ensure there would not be significant disruption, "but inevitably there will be some.".

-RNZ/Jordan Bond.