Thousands more people will now be allowed to return to work if they are a close contact of a positive COVID-19 case, with national cabinet agreeing to expand which workers should be exempt from isolation rules.

Prime Minister Scott Morrison said the exemption would be extended to cover all those working in transport and freight, not just food distribution.

He added it would also include all non-public facing healthcare and support workers, emergency services, teachers and childcare workers and energy and waste management workers.

High-risk close contacts, like those who are living with someone with COVID-19, must take a rapid test every second day until day six of their isolation period.

Those who are considered low risk do not have to have the regular tests, but must monitor for symptoms.

The changes are designed to help ease the pressure on workforces and supply chains which have been under increased strain as infections have skyrocketed and the number of people sent into isolation as close contacts has increased.

"We heard today from the Treasury Secretary [Steven Kennedy] that we could be looking at up 10 per cent absenteeism from our workforce at any one time," Mr Morrison said.

Mr Morrison said the pressure on the workforce would rise if schools did not go back on time, with parents staying at home to look after children.

Queensland and South Australia have both announced plans to delay the start of the school year for most pupils, while New South Wales and Victoria have said their schools will reopen as planned after the summer break.

"If schools don't open, that can add an additional 5 per cent of absenteeism in the workforce," Mr Morrison said.

"It is absolutely essential for schools to go back safely and remain safely open if we are not going to see any further exacerbation of the workforce challenges we are currently facing."

National cabinet agreed to "key principles" about how schools will operate during the current and future outbreaks, with Mr Morrison stressing all leaders agreed them staying open was crucial.

"The first principle is that childcare and schools are essential and should be the first to open and last to close wherever possible, and that face-to-face learning [is] prioritised," he said.

More detail on the plan for schools, including surveillance testing using rapid antigen tests and mask-wearing policies, will be finalised by the leaders next week.

"We had a very extensive discussion about that today with a range of views across states and territories about what the way forward is," Mr Morrison said.

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