Far more people need to get vaccinated against coronavirus before Australians can return to unimpeded domestic travel, West Australian Premier Mark McGowan has warned after closing his state's border with Victoria.
Victoria will enter a seven-day lockdown from midnight on Thursday after a cluster in Melbourne's north grew to 26 cases.
The state is now designated a 'medium-risk' jurisdiction under WA's controlled border regime.
Travel is blocked for anyone who has been in Victoria since May 16 unless they can secure an exemption.
"This is a concerning and a fast-developing situation, however the controls we have already put in place have mitigated the risk," Mr McGowan told reporters.
People who have recently travelled to Victoria and need to return to WA must self-quarantine for 14 days upon returning home.
Those who have already returned after being in Victoria since May 16 are required to get tested within 48 hours and self-quarantine until they return a negative result.
Previously they only had to get tested if they had been to a confirmed exposure site.
Seven people in WA are known to have attended exposure sites in Melbourne, including AFL games at the MCG and Marvel Stadium.
One has returned a negative result and the others are pending.
Just two per cent of WA's population of 2.6 million people has been fully vaccinated against COVID-19, including about half of those aged over 70.
"We need to obviously get far more vaccine rollout before such time as we can look at different measures in place apart from borders," Mr McGowan said.
The premier said international borders should not reopen until everyone who wanted to be vaccinated had been given the opportunity.
Chief health officer Andy Robertson said WA would likely retain the option of border closures until at least the conclusion of phase 2A of the vaccine rollout, which includes all over-50s.
"Until we get to that stage, if we get cases coming into WA we could end up with a significant outbreak with lots of people in hospital," he said.
"So we really have to get through that and that's probably looking at around 70 to 80 per cent of the population vaccinated."
Mr McGowan said 531 people were due to fly to WA from Victoria on Thursday but the number was likely to drop as airlines and passengers adjusted their plans.
He said the wide spread of the virus in Victoria was troubling.
"The concerning pattern of this outbreak is exactly the kind of situation we had in mind when making decisions to lock down WA in the past," he said.
The travel exemption criteria include senior government officials, active military personnel, federal MPs, transport, freight and logistics workers, and individuals approved on compassionate grounds.
WA Health meanwhile said its COVID-19 testing clinics were experiencing high demand.
"If you are a Western Australian who is asymptomatic and who has not recently been to Victoria, please do not present for testing," it said in a statement.