Victorian Premier Daniel Andrews has warned the state will take 'extreme measures' if coronavirus reaches a pandemic phase.

Mr Andrews said all schools would close and entire sectors would be forced to work from home if the COVID-19 crisis further deepens.

He released the plan on Tuesday after three more cases were confirmed in Victoria, including the first locally transmitted.

Victorian Premier Daniel Andrews (left) has warned of the extreme measures the state government will take if coronavirus hits the pandemic level

They bring the state's 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 said.

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.

Elite private school Carey Baptist Grammar School in Kew, in Melbourne's inner suburbs, was closed on Tuesday after an adult member of staff developed symptoms similar to COVID-19

CORONAVIRUS CASES IN AUSTRALIA: 26,651 Victoria: 19,835 New South Wales: 4,166 Queensland: 1,149 Western Australia: 659 South Australia: 466 Tasmania: 230 Australian Capital Territory: 113 Northern Territory: 33 TOTAL CASES: 26,651 CURRENT ACTIVE CASES: 1,340 DEATHS: 810 Updated: 9.56 PM, 13 September, 2020 Advertisement

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.

Elite private school Carey Baptist Grammar School in Kew, in Melbourne's inner suburbs, was closed on Tuesday after an adult member of staff developed symptoms similar to COVID-19 after being in close contact with someone confirmed to have the illness.

'The health and safety of our community is our first priority,' principal Jonathan Walter wrote in an email sent to parents on Monday night.

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

'Carey has been in contact with both the Department of Health and the Department of Education to ensure we have the latest information and advice.

'Based on this advice, Carey has made the decision to close the whole school for the day on Tuesday, March 10 while we assess the situation.'

Carey Grammar is the fourth school in the country to shut down because of the widening coronavirus crisis; the other three are in NSW.

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.