'This nonsense has to stop': McGowan calls on PM to stop supporting Palmer's border fight

West Australian Premier Mark McGowan has labelled Prime Minister Scott Morrison's support of Clive Palmer's border challenge before the High Court as "ridiculous" and unnecessary, and called for a cap on international arrivals to Perth in light of new coronavirus cases brought into the state.

There have been three new coronavirus cases overnight from three domestic flights and three international arrivals from Europe, Doha and Indonesia landing yesterday, taking the total to nine over the past two days. All new cases have been quarantined in hotels.

WA Premier Mark McGowan calls border threat 'ridiculous'.Credit: Nine News

Mr McGowan said the "major threat" to WA was from travellers now choosing to return home and the need to slow the flow as it put pressure on hotels and security staff.

He asked the federal government to cap arrivals coming into WA in the vicinity of one flight every three days and said the state government was also drafting urgent legislation so returning travellers paid for their own 14-day hotel quarantine.

Once the bill was ready, Mr McGowan said he would recall Parliament for a special sitting to get the legislation through quickly.

Mr McGowan said police would also double down efforts at airports over people's exemptions to be let into the state and on border spot checks.

"Our hard border is under threat," Mr McGowan said.

"As we know, Clive Palmer's High Court challenge is being supported by the federal government.

"The announcement today between NSW and Victoria to close their borders is one that I support but the idea that our hard border is being challenged in the High Court is now clearly flawed and completely unnecessary.

"It does not make sense for the federal government to be supporting a border closure between NSW and Victoria but on the other hand challenging Western Australia's border in the High Court of Australia.

"This nonsense has to stop and it has to stop now."

Mr McGowan said WA was an economically free and relaxed state because of its cautious, careful and considered approach, and there was no basis for the Commonwealth to pursue the legal action.

"If they succeed in High Court we would have to bring it down and we would have no protection," he said.

"What I would say to the Prime Minister, Clive Palmer and people of Australia, stop the legal action and allow us to do our job of protecting Western Australians."

He asked for premiers to be able to make their own decisions based on the best interests of their states "without others telling them what to do".

In the meantime, WA is reviewing exemption categories to make them as strict as possible while allowing essential travel, such as freight truck drivers delivering food and mining supplies.

He said WA was tougher than any other state or territory.

Phase 5 of WA's 'roadmap to recovery' was due to come in on July 18 and would lift all restrictions except the strict border or controls over Aboriginal communities, but whether or not to delay its implementation was being examined this week.

Mr McGowan appeared confident it would still go ahead as there had been no evidence of community spread in WA, with the last case more than 80 days ago.

AMA WA president Dr Andrew Miller is calling on the government to hold off Phase 5, as "we can't fool ourselves and think what is happening in Victoria will not happen in WA".

"That is a big risk to our society and we can't get too far ahead of ourselves in thinking we can ease restrictions further, safely at this time; particularly now that we have found out that our ability to track and trace here in Australia is probably not more than about 40 or 50 cases a day for a bit over a week before we run out of capacity," he said.

He supported the Premier's call to Mr Morrison to step away from the High Court challenge to WA's border, saying those arriving from interstate were essentially in the same category as those who arrive from overseas in countries where there remains community spread.

"We need to rejig the way that we think and we need to look at how hard our border really is because there is anecdotally a lot of people coming in this state not being tested, not being quarantined and we need to understand how sustainable that is and what different arrangements we need to put in place."