There are fears Victoria's COVID-19 outbreak could spread interstate after an infected person spent more than eight hours at an airport cafe.
The Brunetti cafe in Terminal 4 at Melbourne Airport was listed as an exposure site early Friday morning, after being visited by the case on February 9 between 4.45am and 1.15pm.
Anyone who visited the cafe during that time needs to get a COVID-19 test and isolate for 14 days.
It brings the total number of exposure sites listed on the Health Department's website to 30.
The outbreak, connected to the Holiday Inn at Melbourne Airport, has grown to 13 cases, sparking fears the city could again go into lockdown.
A total of five new cases were confirmed on Thursday, including two announced at 11pm.
The cases, included in Friday's official figures, consist of a female assistant manager and four close contacts of people who earlier tested positive to COVID-19.
One of the five is believed to have had some contact with Camberwell Grammar School.
"We believe there will be some additional exposure sites emerging from some of these cases," Victoria's COVID-19 Testing Commander Jeroen Weimar said on Thursday.
"That work needs to be done over the coming hours."
Mr Weimar said authorities were "right on top" of the outbreak, picking up cases among identified contacts who had tested negative just days earlier.
Mr Weirmar's "working assumption" is all the cases have been infected with the more transmissible UK variant of COVID-19, complicating the containment job.
"This is by no means over," Mr Weimar said.
"We are still in the opening quarter of the Holiday Inn outbreak, I'm afraid. We've got a lot more work to do."
The rising threat has raised the prospect of Melbourne going into lockdown again, according to the Herald Sun.
Victorian government advisers met on Thursday to consider how this might happen, the news outlet reported on Friday, citing an unnamed source.
AAP understands the government is continuing to hold briefings and meetings on Friday morning.
Prime Minister Scott Morrison said he had not been briefed on whether the Victorian government was planning another lockdown.
"Hotel quarantine is never 100 per cent fail-safe and to suggest it ever will be is just not realistic," he told 3AW radio.
"The issue is how you deal with it when it occurs ... and the response of Melburnians, once again (has been) tremendous."
Mr Morrison said Victorian authorities "should be able to get on top of this like other states have".
"Look at Perth, look at Brisbane, look at Sydney, proportionate short-term responses and they're back on deck."
Jane Halton, who's on the board of the federal government's National COVID-19 Coordination Commission, said while the number of new cases was "worrying" their source had also been identified.
"At the moment we are not seeing reports of any cases that have an unidentified source," she told Nine's Today Show.
"I really hope we don't need to lockdown but everybody right now needs to read that list of what the hotspots are, think about where they have been (and) get themselves tested."
The cluster has prompted several states to tighten borders to travellers from Greater Melbourne.
South Australia locked out travellers from the Victorian capital at midnight on Thursday, while Queensland will bar entry to visitors of the city's exposure sites from 1am on Saturday.
Western Australia also announced its hard border to Victoria would be extended for at least another seven days.
An undeclared nebuliser, used inside the room of an infected family of three at the hotel, is the suspected cause of the outbreak.
© AAP 2021
Photo: Holiday Inn at Melbourne Airport. (AAP Image/Luis Ascui)