Victoria has effectively shut its border to the entirety of NSW and the ACT over concerns COVID-19 could leak out of Sydney.
The state's acting chief health officer has declared NSW and the ACT will become red zones under Victoria's travel permit system from 11.59pm on Sunday.
Previously both regional NSW and the ACT were listed as orange zones, allowing people from those areas to enter Victoria if they got tested and isolated until they returned a negative result.
But they will soon be lumped in the same category as Sydneysiders and those in surrounding areas, hot on the heels of NSW recording 77 new local cases on Sunday.
"Victorian public health authorities are concerned about the risks of transmission beyond current red zones in Greater Sydney and surrounds, and the potential risks this poses to the Victorian community from people entering our state," the health department said.
After Sunday night's deadline passes, Victorian residents will still be able to return from red zones but must isolate at home for 14 days.
The "bubble" arrangement along the Victorian-NSW border remains intact for local residents, though they must continue to travel with proof of address and not enter any red zones.
However, authorities are asking cross-border residents not to travel outside the bubble at any time.
Victorian Premier Daniel Andrews, who grew up living in Wangaratta near the state's northern border, had earlier on Sunday flagged the imminent tightening of travel restrictions with NSW.
"We do not want this virus here in our state," he told reporters.
"I would say to all of those Victorians who are in Sydney and in NSW more broadly, if you're coming home then you better be quick about it.
"Many warnings were given about exactly this sort of outcome."
He also warned people against trying to sneak into Victoria from red zones without the correct paperwork, as police and authorised officers continue to monitor Victoria's land crossings and airports.
"If you do the wrong thing you will be found, you will be fined and you have every chance of becoming very, very famous," he said.
The Australian Health Protection Principal Committee met on Sunday, with Mr Andrews hoping officials would agree to a national border approach with NSW.
But, in the absence of that, he said Victoria would act independently if their experts deemed it necessary.
"I won't hesitate to do it," Mr Andrews said.
While acknowledging it was within the state's power, Chief Medical Officer Paul Kelly said the Commonwealth did not support shutting the NSW border.
"It's not an easy thing to do to close the border with NSW," he told reporters in Canberra.
"There are many, many places that people can cross that border so I'm sure it will be a decision not taken lightly."
The border decision came as Victoria recorded its 11th day in a row without a local case of COVID-19 on Sunday, as well as no new infections in hotel quarantine.
Some 23,300 tests were processed in the 24 hours to Sunday morning, while almost 13,000 Victorians received a vaccine dose at one of the state-run hubs.
A Qantas flight from Launceston to Melbourne on July 2 remains the state's only listed exposure site.
A healthcare worker was on the QF1542 flight en route to London, where she tested positive two days later.
All those aboard the domestic flight must get tested and isolate until they receive a negative result.
