National cabinet has agreed to halve overseas arrivals to ease pressure on the quarantine system.

Jane Halton, who chairs the global alliance on epidemic preparedness, said she was disappointed by the decision.

"What I am concerned about is the number of people offshore who are still vulnerable," she told ABC radio.

"I do think we have to find a compassionate way to deal with these very, very difficult cases."

At least 34,000 Australians remain stranded overseas and desperate to come home.

Almost 4000 of them are considered vulnerable.

Ms Halton's review recommended the expansion of purpose-built quarantine facilities and the introduction of national standards.

She would not be drawn on whether the Commonwealth had been too slow to act on quarantine sites.

"I would have preferred if we had been in a position to open, for example, the Victorian centre earlier," she said.

"That's not where we are but they are moving now unbelievably quickly and they will have a purpose-built facility. That's a very important part of this rollout."

However, Ms Halton does not expect any of the purpose-built sites to be operating by the end of the year.

"If we can tighten up hotel quarantine and get more people in, I think that would be good," she said.

There have been at least 26 breaches of hotel quarantine throughout the coronavirus pandemic, leading to widespread outbreaks and lockdowns.

Australian Associated Press