Victorians have been told all their schools may be closed and entire sectors forced to work from home when the coronavirus reaches a pandemic phase.
Premier Daniel Andrews has warned the measures are laid out in the state's COVID-19 pandemic plan, released on Tuesday.
Another three cases of coronavirus were confirmed in Victoria on Tuesday, including the first locally transmitted.
They bring the total number of coronavirus cases to 18.
Mr Andrews says it is not a matter of if but when Victoria will move into a pandemic phase with rapid transmission of the virus.
"We will need to ask Victorians to do things we have never asked them," he told reporters.
The plan includes the "inevitability" all schools will close for some time and entire sectors or workforces will have to work from home, he said. Big events will also have to be called off.
"Now's not the time for those things but that time will come and it's appropriate, just like fire - to be frank with people."
Of the latest cases, two are men in their 70s, one who returned to Melbourne from Singapore on flight EK404 on Friday, and the other from Los Angeles on flight VA24 on Sunday.
A woman in her 50s is also now isolated at home, after being in the same household as a confirmed case who returned to Melbourne on flight UA60 from the US on February 28.
Victorian Health Minister Jenny Mikakos said it is the first case of local transmission with more expected.
The woman works at Carey Baptist Grammar School in Kew, which was closed on Tuesday after she developed symptoms.
Seven COVID-19 screening clinics are now open in Victoria, including one at the Royal Melbourne Hospital, where lines of people in masks could be seen awaiting tests on Tuesday.
One Melbourne doctor - former Australian Medical Association president Mukesh Haikerwal - has resorted to screening patients in cars outside his Altona North practice.
Victoria's dedicated COVID-19 phone line and the Nurse-On-Call Hotline both crashed on Tuesday due to an influx of calls.
Another 50 staff will be brought on deck for the coronavirus helpline on Wednesday, with an additional 100 by week's end.
© AAP 2020