Melbourne Airport has been put on alert after traces of the Omicron super variant were found in the wastewater - as Victoria records four suspected cases of the highly infectious strain. 

Health authorities confirmed three of the four suspected Omicron infections have been out in the community.

Two suspected cases had already been reported on Wednesday but Victoria's department of health confirmed they were notified of another two on Thursday.

Workers and travellers who visited the city's airport have now been urged to monitor for symptoms and get tested as soon as they appear.

'The samples from two airport catchments were collected on 1-2 December and are consistent with a known suspected case of the Omicron variant who visited the airport,' the health department said. 

Authorities say they are speaking with the suspected case and notifying any close or casual contacts.

'A number of contacts have been identified and instructed to quarantine for seven or 14 days based on their vaccination status,' they said.

'Other people of lower risk have been instructed to get a test and isolate until they receive a negative result.

Further contact tracing work is ongoing and is likely to produce more contacts.'

The four suspected Omicron cases are from Casey in Melbourne's outer southeast, Wyndham in the outer southwest, and two in Brimbank in the west.  

It comes after Victoria on Wednesday recorded its first confirmed Omicron case among an international traveller from the Netherlands who arrived in Melbourne on December 3 and went directly into hotel quarantine.

Premier Daniel Andrews has reiterated the state is not chasing an 'Omicron zero strategy', describing it as unachievable and not the 'smart thing to do'.

'This thing is in our country and will be more widespread than any surveillance will show you,' he told reporters on Thursday.

'That's just the nature of this virus.

There's always more cases than you know about.'

While health experts are trying to learn more about the variant since it was observed in South Africa, Mr Andrews noted early evidence suggested it was milder than the Delta strain and current vaccines are not compromised.

The premier has received no health advice to reimpose some restrictions to quell an Omicron outbreak, akin to those announced in the United Kingdom.

'They're having to have conversations about lockdowns and conversations about all sorts of things because they're at 60 or 65 per cent double dose, not 95 per cent double dose,' he said.

Some 91.8 per cent of Victorians 12 and over are now fully vaccinated and daily COVID-19 cases remain steady in the 1000s with hospitalisations in the low 300s.