Western Australia will close its border to Victorians from New Year's Day, as more COVID-19 cases emerge in Melbourne.
The government has revised Victoria's status to one of medium risk, effectively barring travel to WA.
Only people granted exemptions will be allowed to enter, while West Australians returning home will be required to quarantine for 14 days.
Any Victorians who arrived in WA on or after December 21 will also need to self-isolate for 14 days from when they first entered the state.
They will also have to take a coronavirus test on day 11 or at any time if they develop symptoms.
The same rules are already in place in regard to NSW.
Acting Premier and Health Minister Roger Cook said the new measures were based on the latest health advice.
"Clearly we are dealing with an unpredictable situation that is likely to get worse before it gets better," Mr Cook said on Thursday.
"The timing is terrible but COVID-19 doesn't respect dates."
The border closures come after Victoria revealed its cluster of virus cases had grown to eight, prompting it to also close its border to NSW.
