Professor Imogen Mitchell, who is the clinical director of the ACT COVID-19 response, said the ACT was left vulnerable as the nearest intensive care unit was 300 kilometres away.

It came as ACT Chief Minister Andrew Barr said the territory risked thousands of cases and an overwhelmed health system if the city opened up when 70 per cent of the population was fully vaccinated.

National cabinet was reportedly shown new modelling on Friday afternoon, which showed that medium public health measures would need to stay in place until Australia reached the 80 per cent fully vaccinated milestone if case numbers are high.

The ACT reported 30 new COVID-19 cases on Friday, which is the second equal highest day of case numbers for the territory. Alarmingly, at least 14 were in the community for part of their infectious period.

Nineteen cases have been linked to previous cases and the remainder have not yet been linked. There are eight people with COVID-19 in hospital in the ACT. One person is in intensive care and requires ventilation.

Mr Barr said it was too early to tell whether the high number was a one-off.

"It is clear that is not a good number," he said.

"While we have a high number of cases infectious in the community, our case numbers will continue to grow."

As school holidays start, the territory will ramp up its border patrol measures, as Mr Barr revealed the Australian Defence Force has been brought in to help at checkpoints along the ACT-NSW border.

Cases in the surrounding NSW capital region also had a spike on Friday with 17 cases reported in the Southern NSW Local Health District, including three in Queanbeyan and two in Googong.

Mr Barr said the ACT had a responsibility to care for patients in this region as concerns grow over modelling on hospital capacity, which the Chief Minister said looked "quite scary".

He suggested the territory's health system would be overwhelmed if lockdown ended when 70 per cent of the population had two doses, based on the territory's current caseload.

"We could anticipate if we opened up at 70 per cent case numbers in the thousands every day and that would be an alarming figure and we'd overrun our health system," Mr Barr said.

Prior to national cabinet on Friday, Mr Barr said he wanted answers about what would happen when NSW eased restrictions once 70 per cent of the over 16 population were fully vaccinated.

"What's going to happen when NSW open up [and] ease restrictions at 70 per cent double dose," Mr Barr said.

"The modelling would indicate that case numbers would go from thousands into the tens of thousands each day.

"That could be very challenging."

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Professor Mitchell said modelling is a "variable feast", warning there is no way of predicting exactly how much strain will be placed on the territory's system.

"There's no doubt there is a significant flow-on effect from NSW opening in a greater way," she said.

"Some of the numbers that have been generated out of the modelling are extremely concerning ... But the difficulty really is it's impossible to predict until it really does happen."

The national plan may need to be reworked after it was reported modelling showed medium public health measures would need to be in place until the 80 per cent vaccine threshold is reached if cases are high. The Guardian reported the modelling was shown to first ministers at Friday's national cabinet meeting.

Examples of medium public health measures include increased retail activity, limited seated dining at restaurants and a five-person limit on household visitors. Relaxed stay-at-home orders would also apply, which would allow people to leave for work, study and essential purposes.

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