Treasurer Ben Wyatt on Thursday unveiled a budget headlined by a massive $27 billion infrastructure spend and a $1.2 billion surplus this financial year.

But it remains a mystery when the state's hard borders will come down, despite WA Treasury bureaucrats nominating the same reopening date as this week's federal budget.

"If Treasury had said 'rather than the June quarter next year, make an assumption that it's the December quarter this year', it would have a very benign impact on the assumptions," Mr Wyatt told reporters.

"What you are seeing, because of the changed behaviour of people travelling and people consuming, is that for 2021, the impact is marginal."

Business groups and West Australians separated from their loved ones are desperate for clarity on when free travel between the states will be allowed.

But for all the interest in the border situation, it was consigned to a footnote in the almost 1500-page budget documents.

"It is stressed that these are Treasury assumptions for forecasting purposes only, rather than government policy," the footnote said.

That's unlikely to stop people from latching onto the April 1 date given the government's refusal to set a timeframe for the restrictions being lifted.

"And they shouldn't, because it's not the government policy," Mr Wyatt said.

"The government policy is still very much focused around the health advice.

"Treasury had to make a call and by chance, that sort of ended up replicating the Commonwealth's position on that."

Prime Minister Scott Morrison on Thursday said WA's geographic and economic situation was clearly different to that of the eastern states.

But he warned that the borders would need to come down eventually.

"The only reason to have a border is on health grounds and even with COVID-19, the protection against COVID-19 can't be a border," he told Perth radio 6PR.

"It has to be your public health response capability."

WA has now gone almost six months without any community spread of COVID-19.

Under current health advice, the borders won't reopen until the eastern states go 28 days without community spread.

Both Victoria and NSW have continued to record "mystery" cases.

Authorities have warned that because WA has largely removed restrictions on physical distancing and large gatherings, it would only take one case coming in from the eastern states to generate a large uncontrolled outbreak.

WA recorded two new cases on Thursday, a man and a woman in their 30s in hotel quarantine who travelled to Perth from overseas.

The state has 11 active cases.

Australian Associated Press