Queenslanders will be locked out of Western Australia after the McGowan government moved to reintroduce a hard border.
From 1201am local time on Tuesday, travellers from Queensland will be prevented from entering WA unless they have an exemption.
The hardline measure also applies to anyone from other states who has been in Queensland since March 27.
Greater Brisbane has been ordered into a three-day lockdown after a coronavirus cluster grew to seven cases with evidence of "significant community transmission".
WA had already ordered all recent arrivals from Queensland to get tested and self-isolate for 14 days.
The exemption criteria include senior government officials, active military personnel, federal MPs, transport, freight and logistics workers and individuals approved on compassionate grounds.
Premier Mark McGowan says the decision to reclassify Queensland from low to medium risk is based on health advice.
"We've been monitoring the situation closely and have scaled up our border controls as required, to keep our community safe," he said in a statement on Monday.
"The hard border measure is necessary and is our best defence in keeping the virus out.
"It's going to be disruptive for many people and put many people's plans in disarray, however we need to put the health of our WA community first."
Mr McGowan said recent arrivals from Queensland, including those arriving before midnight on Monday, were free to depart WA.
"We are thinking of our friends and family in Queensland as they go into lockdown this evening," he said.
"They are doing the right thing to keep Queensland safe and protect us all across the country."
Anyone who arrived from Queensland between March 20 and 26 will be contacted by police using the G2G pass system and advised of the latest exposure sites in Queensland and Byron Bay.
People who have been to those sites must also get tested and self-isolate.
But quarantine is currently not necessary for anyone who has come into contact with recent arrivals from Queensland.
WA recorded three new cases overnight, all in hotel quarantine.
