Victoria has had no local cases of coronavirus for a 13th consecutive day, although there are four in hotel quarantine, three linked to the Australian Open.

Victoria has recorded no new locally acquired cases of coronavirus for a 13th consecutive day, although there are more infections among Australian Open players and staff.

Premier Daniel Andrews on Tuesday confirmed there are four new cases of COVID-19 in hotel quarantine, three of which are linked to the contingent in town for the grand slam.

It brings the number of active infections in the state to 34, an increase of one.

More than 70 players - almost a fifth of those taking part in the Australian Open - have been forced into strict quarantine after nine people on their charter flights to Melbourne tested positive for COVID-19.

But the premier has indicated some of the cases linked to the tournament will be reclassified as non-infectious shedding.

It could mean some players will be allowed to leave their rooms for training.

"If you've got say 30 people who are deemed a close contact because they've been on a plane with a case, and the case is no longer an active case but a historic shedding, well that would release those people from that hard lockdown," Mr Andrews told reporters.

Victoria's Chief Health Officer Brett Sutton has warned the virus could still be incubating in some of the 1200 people who have arrived in Melbourne for the Open since Thursday.

Cases have been linked to three flights, from Abu Dhabi, Doha and Los Angeles.

"People may still turn positive, obviously the last exposure was when they last left their country of origin or indeed on a flight where there was a case," Professor Sutton said on Monday.

"So there might be some more positives in coming days but that that will take place over time."

Meanwhile, 25 of Sydney's 35 local government areas were downgraded from "red" to "orange" zones at 6pm on Monday as part of Victoria's "traffic light" permit system.

The Blue Mountains and Wollongong also moved from red to orange, while 16 local government areas along the NSW-Victoria border changed from orange to green, permitting unrestricted entry.

People travelling from an orange zone still need to apply for a permit online and get tested within 72 hours of their arrival in Victoria, isolating until they receive a negative result.

It follows the downgrading of Greater Brisbane from red to orange at the weekend.

Sydney local government areas Blacktown, Burwood, Canada Bay, Canterbury-Bankstown, Cumberland, Fairfield, Inner West, Liverpool, Parramatta and Strathfield remain red zones for now.

The 10 areas were all linked to Sydney's Berala cluster, which totals 35 cases.