A man infected with coronavirus travelled through Victoria and South Australia before testing positive in NSW.
Victorian Health Minister Martin Foley on Monday revealed NSW Health alerted their Victorian counterparts late on Sunday night to the man, who was infectious during his travels.
The man, who is a removalist, went through the states for work. He stayed overnight in Victoria on July 8 then drove to South Australia before returning to NSW.
Mr Foley said his department is in contact with NSW's department to get the full list of local exposure sites.
It's believed the man did travel through Melbourne.
"Our friends in Sydney are facing really challenging circumstances, and we wish them every success in their fight," Mr Foley said.
"This is now the third incursion into Melbourne and Victoria as a result of this outbreak, we've run the other two down."
Removalists are permitted workers under the state's border permit system.
It comes after Victoria recorded its 12th day of no locally acquired cases and the state shut the border to NSW and the ACT overnight, declaring them red zones under the travel permit system from 11.59pm on Sunday.
Victoria's acting chief health officer cited concerns about the risk of coronavirus transmission beyond Sydney and surrounding areas for the decision.
NSW reported 112 new local cases on Monday.
The border closure announcement was made just after 4pm 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, encouraging residents to return home urgently.
Victorian residents who missed Sunday's deadline will still be allowed to enter the state but must isolate at home for 14 days.
In addition, the Victoria-NSW "border bubble" arrangement will remain intact for local residents, though they must continue to travel with proof of address.
Victorian authorities are also asking cross-border residents in both states not to travel outside the bubble at any time.
© AAP 2021