Victoria is establishing a permit system for NSW travellers and banning arrivals from "red zone" areas, as Sydney's northern beaches cluster worsens.
Health Minister Martin Foley on Friday announced the new "traffic light system" for NSW arrivals will come into effect from midnight in the wake of the outbreak growing to 27 cases.
Anyone who lives in or has visited the northern beaches or other "red zone" locations will not be permitted to enter the state.
If they do, they'll be treated as an international traveller and taken from the airport to hotel quarantine for 14 days.
Greater Sydney (orange zone) residents will be encouraged to get tested and self-isolate until producing a negative result, while those from regional NSW (green zone) are asked to monitor for symptoms.
The permits will be made available online and requested by health officials when NSW passengers land at Melbourne, Albury, Mildura, Bendigo and Avalon airports.
Police patrols will also be roving the road borders.
With the NSW outbreak expected to deteriorate, Mr Foley strongly advised Victorians not to travel to Sydney.
"It won't be the Christmas or the holiday you were planning," he told reporters.
Mr Foley said the rapidly evolving situation meant it was possible Victorians could be forced to undergo a fortnight in quarantine upon their return.
There are 47 flights from Sydney scheduled to arrive in Melbourne on Friday, with health department officials spot-checking those planes.
Passengers are being asked if they've visited the northern beaches or the other listed hotspots and, if so, being directed to get tested and self-isolate immediately.
Victoria's Chief Health Officer Brett Sutton said a person now in Victoria had come forward to identify themselves as a close contact of the northern beaches outbreak.
They are not showing symptoms and haven't tested positive, but have been placed in hotel quarantine due to being unable to safely self-isolate.
It could be weeks until the outbreak is brought under control, Mr Sutton said, as avenues for transmission play out over the coming days.
However, he said the public should be reassured as most cases appear linked through visitors to the Avalon Bowling Club and RSL club.
Victoria has now gone 49 days without a locally acquired case of COVID-19.
Another infection was recorded among a returned traveller on Friday, the eighth since the state restarted its new-look hotel quarantine program on December 7.
