South Australia and Western Australia have slammed their borders shut to NSW after the number of coronavirus infections linked to a Sydney outbreak grew to 31.
South Australian Premier Steven Marshall said the situation in NSW was deteriorating and immediate action had been taken to keep South Australians safe.
The ban will not apply to essential workers, returning South Australians and other people granted exemptions.
There will also a 100-kilometre buffer zone along the border to allow people living in close communities, including Broken Hill, to still travel into SA.
"It's unfortunate that this has to be done. We do recognise this causes a significant impact on people," SA Police Commissioner Grant Stevens said.
"Clearly, the advice from SA Health has created an elevated level of concern."
Mr Stevens said people already in transit to SA, by air or road, would be managed at the airport and on the border and either granted exemptions or turned around, depending on their individual circumstances.
People allowed to stay may be still required to quarantine for 14 days.
The reintroduction of Western Australia's hard border came into immediate effect on Wednesday, reclassifying NSW as a "medium-risk" jurisdiction.
Travel from anywhere in NSW is no longer permitted except for exempt travellers including senior government officials, active military personnel, federal politicians and freight workers.
Exemptions may also be granted on compassionate grounds including for West Australians who need to return home.
Those travellers must self-quarantine for 14 days upon arrival and present for two coronavirus tests during that period.
The edict applies to anyone who has been in NSW since 12.01am on June 11, including those who have since travelled through other jurisdictions including the ACT.
"Naturally these immediate changes will cause inconvenience but the hard border is necessary to protect the health of Western Australians," Premier Mark McGowan said.
"I want to thank everyone for their understanding."
People who arrived from NSW prior to the hard border should continue to comply with existing directions, including 14 days' quarantine for anyone who has visited exposure sites.
NSW recorded 13 new cases on Wednesday, eight of whom attended a weekend birthday party which has been labelled a "super-spreader event".
The so-called Bondi cluster now stands at 31 after an unvaccinated Sydney airport limousine driver last week tested positive to the highly infectious Delta variant, which quickly started spreading at a busy shopping centre.
Residents who live or work in seven local government areas cannot travel outside the metropolitan area unless it's absolutely essential.
Queensland, Victoria and New Zealand have also imposed bans on travel from much of Sydney.
Mr McGowan has indicated WA's quarantine restrictions for Victorians are likely to soon be eased given that state's outbreak has largely been contained.
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