Western Australia has banned entry to travellers from South Australia after elevating the other state's risk rating from "low" to "medium".
The hard border with South Australia came into effect at 12.01am, with travel from SA not permitted unless the person is an approved traveller.
The exemption list is limited to certain officials, a government statement on Thursday night said.
Any West Australian who recently travelled to SA is able to return under compassionate grounds, but must apply through the G2G pass system.
Approved travellers must have proof of a negative COVID-19 PCR test, be fully vaccinated, able to self-quarantine for 14 days and get tested within two days of arrival.
Premier Mark McGowan said the situation in South Australia was concerning and the hard border needed to be reinstated while Western Australia got its vaccination rates up.
"I'm aware this will be disruptive to many and present challenges to some however we must do everything we can to protect the health of Western Australians," he said in a statement.
South Australia reported 18 new COVID-19 cases on Thursday, its largest single-day tally for more than a year.
Health Minister Roger Cook said the surge in positive cases in South Australia meant swift action was needed to stop the virus entering Western Australia.
"We've seen the health, social and economic pain the virus can wreak in communities on the east coast and that is why it is vital we don't fall at the last hurdle, as we countdown to an announcement on when we will safely reopen to the world," he said.
Queensland and Tasmania are the only states not subject to travel restrictions in WA, which has largely kept visitors out for more than 18 months.
The reopening of state borders is expected to align with WA achieving 90 per cent full vaccination. A firm date is set to be announced sometime after next Friday's national cabinet meeting.
Australian Associated Press
