Victoria is on high alert after a man from NSW with COVID-19 travelled through the state and South Australia while infectious. The removalist stayed overnight in Victoria on Thursday before driving to SA and later returning to NSW, where he tested positive on Sunday.
Victorian Health Minister Martin Foley said NSW Health alerted the state's authorities late on Sunday night. Contact tracers are working to establish the man's movements, though it is believed he travelled from Sydney to Melbourne via the Hume Highway and worked at several homes in the city before travelling to SA.
"We would expect there will be exposure sites and we expect there will be people who require to quarantine," Mr Foley said.
Removalists are permitted workers under the state's border permit system.
Mr Foley said the risk of the virus spreading from NSW to Victoria was "very real".
"This is now the third incursion into Melbourne and Victoria as a result of this outbreak. We've run the other two down," he said.
It comes after Victoria recorded its 12th day of no locally acquired cases and the state effectively shut the border to NSW and the ACT overnight, declaring them red zones under the travel permit system from 11.59 pm on Sunday.
ACT Chief Minister Andrew Barr said it was "incredibly disappointing and frustrating" Canberra was classified the same as Sydney, despite recording no community COVID-19 cases for more than a year.
But Mr Foley said the rationale behind the decision was "simple", noting the ACT is surrounded by regional NSW. NSW reported 112 new local cases on Monday, it's highest daily total since the Bondi cluster emerged on June 16.
The border closure announcement was made just after 4 pm on Sunday, giving little time for people to return on their existing orange zone permits. But Victorian authorities had been foreshadowing a blanket NSW red zone declaration for days.
Victoria Police's Acting Deputy Commissioner Michael Grainger said an extra 90 officers had been sent to the border, on top of the 260 operating there since last week.
Police are continuing to keep border travellers guessing, adopting a strategy of roving patrols, pop-up checkpoints and the air wing division scanning from Mildura to Mallacoota.
Mr Grainger said 99.9 per cent of the 28,000 people stopped at the NSW border since the operation began on June 25 had been compliant, with only six fines handed out thus far.
Two were issued overnight including one to a Dandenong man who had travelled from a red zone and was spotted in Gippsland when he was supposed to be isolating.
Victorians in NSW are still allowed to enter the state but now must isolate at home for 14 days.
In addition, the Victoria-NSW "border bubble" arrangement will remain for residents, though they must carry proof of address and stay within the bubble.