Authorities are trying to track down up to 5000 people potentially exposed to coronavirus at Melbourne Airport's Jetstar terminal.
In what's been described as the most concerning case in the current outbreak, a woman infected with the virus served hundreds of customers when she worked at the terminal's Brunetti cafe - and many would now be interstate.
The woman worked at the cafe on Tuesday, February 9, between 4.45am and 2pm.
"We believe at that point they may well have been infectious," said Victoria's virus testing boss Jeroen Weimar.
Mr Weimar stressed the cafe worker had followed the testing rules, getting tested on Wednesday before returning a positive result on Thursday, but the virus was moving too quickly.
It's estimated up to 5000 people passed through terminal four during the exposure period on about 29 flights.
Anyone who was in the terminal at that time must get tested and isolate for 14 days.
Authorities are going through flight manifests and looking at staff lists to try and contact airport and retail workers.
"It's critical that we run this to ground now, that we stop it here," Mr Weimar said.
The exposure event has been one of the factors behind the Victorian government's decision to impose a snap five-day hard lockdown statewide.
Other states have once again begun to impose their own restrictions.
Anyone currently in NSW who has been in Victoria on or after Friday, January 29, is being told to stay home for five days.
Western Australia has reinstated its hard border with Victoria for 72 hours from 6pm Friday WST.
Queensland will close its border to Greater Melbourne from Saturday.
An estimated 1500 people who went through the terminal are now in Queensland, and the state's health authorities say contact tracers have been in touch with those people.
The airport exposure comes on top of more than 900 close contacts already connected to the Holiday Inn outbreak, as well as close contacts linked to the Grand Hyatt outbreak.