Premier Steven Marshall says the change, from midnight on Tuesday, means people from those states will no longer be required to quarantine for 14 days when they arrive in SA.

He says people who recently arrived from those states and are already in isolation, are also free to move into the wider community.

At this stage border restrictions related to NSW, Queensland and Victoria will be lifted on July 20, though SA is looking to an earlier date with Queensland.

Mr Marshall said the state government had also received legal advice that what it was proposing could be implemented.

"Every premier and chief minister needs to make decisions with regards to their own legal advice," he said.

"But we've received our advice and it's pretty clear there's no reason for us to be unnecessarily detaining citizens from Western Australia, the Northern Territory or Tasmania."

But WA Premier Mark McGowan hosed down talk of a potential travel bubble with SA and the NT, saying his government had received Commonwealth advice that such a move would breach the constitution.

"It's unconstitutional to pick and choose between the states, so we'd be breaking the law were we to try and do an arrangement with South Australia or the Northern Territory," he told reporters in Perth.

Tasmania and the Northern Territory were also reluctant to immediately respond to SA's decision.

NT Chief Minister Michael Gunner said his government would stick to its original timetable with a review of state borders by the end of this week.

He said officials were monitoring what was happening in other states every day.

Tasmanian Premier Peter Gutwein said he still expected to lift border restrictions towards the end of July, "all things going well" with a decision to be announced on June 26.

"Until then our focus remains on a gradual easing of our broader restrictions to ensure we're well placed to manage any risk associated with coronavirus," Mr Gutwein said.

In other SA moves, up to 300 people will be allowed at all public gatherings from Friday and indoor fitness, dance and exercise classes will be allowed to have 20 people, up from 10.

Deputy chief public health officer Mike Cusack said with more restrictions being lifted, there was always the potential for new virus infections.

"We must not lose sight of this, we must not be complacent," Dr Cusack said.

"We need to recognise that there will be further cases. We are drawing up plans in relation to how we would respond to a case, or to five cases or to 10 cases."

SA reported no new COVID-19 cases on Tuesday, taking to three weeks the period without a new infection.

It has no active cases remaining.

Australian Associated Press