Billionaire Clive Palmer has claimed the WA Government would "destroy the lives of hundreds of thousands of people for decades" if it continued with its hard border restrictions.
The comments came as WA Premier Mark McGowan again expressed his frustration with Mr Palmer's legal challenge against the border closure.
"It's just grossly irresponsible, it's not reflecting the will of the people, it's putting at risk all of our achievements," Mr McGowan said.
"It's so annoying, it drives me nuts."
The legal challenge has been heard in the Federal Court this week, with the High Court expected to make a ruling on the hard border arrangements later this year.
Mr Palmer took to Twitter to attack the WA Government's policy.
"Following revelations that a targeted quarantine was sustainable and there was no reason why the borders could not be open to other states whose performance at containing the virus was better than WA's, it is clear that the closure is motivated by political reasons," he said.
'They want chaos': Palmer
Mr Palmer appeared to be referring to a report prepared by ANU Professor Peter Collignon, in which he said a targeted quarantine regime aimed at travellers from virus-affected areas was more effective than a hard border.
He also told the court hearing a travel bubble between states that had eliminated Covid-19 for 28 days would present minimal risk to the WA community.
He agreed under cross examination that a hard border was more effective than a targeted regime, but was not sure by how much.
"What is going to happen to West Australians when the Federal Government's money tap runs dry?" Mr Palmer asked on Twitter.
"This is the typical negative attitude of Labor, they want chaos, they want states fighting states.
"The WA Premier can't cope with the fact that my legal challenge is being assisted by the Federal Government."
Mr Palmer also made comparisons between the COVID-19 death toll, and the number of deaths caused by influenza and road accidents.
"WA desperately needs courage in leadership and the ability to rebuild the economy now," he said.
Government pins hopes on plan A
Mr McGowan said the state's quarantine system was robust and the Government was doing everything it possibly could to keep COVID-19 out.
"Today there's new cases in Queensland … new cases have come from the southern states into Queensland. Victoria has a diabolical and tragic situation on its hands," he said.
"We do not want that to come in here. We're doing everything we can to prevent that from coming in here.
"Obviously if we end up in a New South Wales or Victorian situation, that will mean big closures of industries, communities and the like. I just do not want us to end up in that position."
The Premier said the Government was confident about its position in regards to the legal challenge.
"We're very hopeful we'll be successful … we'll go to plan B if we lose but at the moment, we're fighting for plan A," he said.
"If the High Court rules the border comes down, we'll look at whatever we can do to protect people.
"It's just so selfish and so irresponsible of Mr Palmer, joined by the Liberal Party, trying to bring down our border."
But Mr McGowan said a decision was not expected from the High Court until September at the earliest.
He repeated his call for the Liberal Party to withdraw from the case, saying the border closure was creating jobs and allowing WA to get its economy back on track far more quickly than any other state.
