No cases of community transmission have been recorded in Victoria as the state closes itself off from Darwin.
Greater Darwin - including Darwin, Palmerston and Litchfield - will be designated a red zone under Victoria's travel permit system from 8pm on Sunday.
The concern is linked to a COVID-19 outbreak at a Northern Territory mine, from where three miners returned to Victoria and are now in isolation.
Victorian health authorities said in a statement non-Victorian residents who have been in a red zone cannot enter the state. Residents can obtain a permit to return and self-isolate for 14 days.
Chief Health Officer Brett Sutton said he was monitoring the public health situation interstate as COVID-19 outbreaks occur in Darwin as well as Greater Sydney, southeast Queensland and Perth.
Greater Sydney and surrounding regions, as well as Greater Darwin, are the only current places declared "red zones" by Victoria.
Victoria and Australia's eastern states also remain on high alert after a domestic flight attendant tested positive for COVID-19.
Melbourne Airport terminals two and three, as well as an airport cafe, have been listed as exposure sites, and those who visited during times of concern on Friday and Saturday are urged to get tested and isolate.
Five Virgin Australia flights on Friday and Saturday took passengers either to or from Brisbane, Melbourne, Sydney and the Gold Coast.
Those on Flight VA334 from Brisbane to Melbourne on Friday afternoon have been ordered into isolation for 14 days.
A total of 128 passengers have been identified and health authorities are in the process of contacting them on Sunday, COVID-19 response commander Jeroen Weimar said on Sunday.
The flight arrived at 5.20pm and the staff member stayed at the Holiday Inn Express at Southbank, which is being deep-cleaned.
"We're working with her and Virgin to ensure that anybody who has had potential exposure is being followed up," Mr Weimar said.
Victoria recorded three new cases acquired overseas, more than 20,000 tests and close to 15,000 vaccine doses administered in the past day.
It comes as Health Minister Martin Foley emphasised the beefed-up police presence on the Victoria-NSW road border on Saturday.
About 1500 Victorians have applied for a red border permit in the past 24 hours, all of whom will be required to isolate for 14 days if they're granted entry.
Police have stationed extra officers at the interstate border and are conducting spot checks and using number plate recognition technology.
Contract tracers are working to make sure the Sydney infections do not spread to Victoria after a man in his 60s flew in from the northern city last weekend after attending what authorities have since dubbed a "superspreader" party.
The man is a worker at a drycleaner in Sandringham and infected his boss, Henry Li.
The men's infections sent a few hundred primary close contacts into isolation, including a building of residents in Oakleigh where the first man lives. Prof Sutton said all residents have returned negative results and can now leave isolation.