Scott Morrison is confident premiers won't rush to close state borders again as NSW authorities race to solve the puzzle created by six new cases of coronavirus.
The prime minister has been so confident domestic borders will stay open the latest federal budget figures have Western Australia as permanently open to the rest of the country.
Mr Morrison says Australians are happy the country is open.
"I think Australians are going to work hard to keep it that way, and I think premiers and chief ministers are very keen to achieve that as well," he told reporters in northern NSW on Thursday.
But West Australian leader Mark McGowan says he won't hesitate to again block NSW travellers to his state, depending on the health advice.
"I realise that would be very upsetting, very upsetting for many people," he told reporters in Perth.
"But if the medical advice says that's what we need to do to protect Western Australia, we will do it. And we will do it immediately."
Treasurer Josh Frydenberg has warned Mr McGowan against doing so, pointing to consumer confidence falling when South Australia had a strict lockdown for a few days.
"That is the one thing that dents confidence, if you have stop-start restrictions, lockdowns or border closures," he told reporters in Canberra.
"Australia is opening up and the recovery is under way."
There are now five cases in a virus cluster in Sydney's northern beaches, including a residential aged care worker and a man who recently performed in a band at various RSL clubs.
Authorities are starting to link the cases together but are yet to discover the source of the infections.
More detailed scientific analysis of the cases is expected by Thursday evening.
A case in Sydney's south - a man who drives international airline crews to and from Sydney Airport - surprised officials on Wednesday.
It was the state's first virus case in the community for close to two weeks and has prompted efforts to tighten regulations for cabin crew of international flights.
Queensland only fully opened the state border to greater Sydney earlier this month after it had been closed since August.
Some states also rushed to snap their borders shut to South Australia when its Parafield cluster appeared threatening.
NSW Health Minister Brad Hazzard has urged people on Sydney's northern beaches to get a COVID-19 test for even the slightest of symptoms.
"Don't feel guilty or bad about going and using the local public health services - we want you to," he told reporters in Sydney.
Meanwhile, the Victorian ombudsman said locking public housing residents in their homes without notice is a breach of human rights laws.
Victoria's government has been told to apologise - and refused - for taking the drastic measure earlier this year.
About 3000 people in nine public housing blocks were prevented from leaving their homes as Victoria's deadly outbreak took off in July, with some locked down for two weeks.
Australian Associated Press
