NSW travellers will need a permit to enter Victoria from midnight Friday, while anyone who has visited Sydney's northern beaches will be denied entry.

While those in the ACT won't need a permit to enter Victoria directly from the territory, residents driving through NSW to the state's border will also be subject to the travel restrictions.

The ACT government said residents should monitor the situation carefully as restrictions could quickly change.

"Canberrans currently interstate and here at home, are encouraged to keep up to date on the situation that is evolving with the northern beaches cluster so they can make informed decisions about any upcoming travel plans," a spokesperson said.

Meanwhile Sydney's worrying northern peninsula virus cluster has grown to 28 cases and is expected to get bigger.

Victoria's new "traffic light" permit system means anyone who has been to the northern beaches or other "red zone" locations since December 11 will be shut out or forced to quarantine in a hotel on arrival.

People from the greater Sydney "orange zone" will be asked to take a test and self isolate, while regional NSW "green zone" residents will be asked to monitor for symptoms.

Anyone from NSW who is in Victoria and has even the slightest symptoms is being urged to get tested immediately.

Victoria's Health Minister Martin Foley says anyone travelling from Sydney should not visit Victoria.

"If you are coming from Sydney and you don't have to come, please don't come," he said.

At the same time, Mr Foley strongly advised Victorians not to visit Sydney, warning they may be forced to quarantine when they return.

"It won't be the Christmas or the holiday you were planning," he told reporters.

Permits will be available online and Victorian authorities will check them from midnight Friday in Melbourne, Albury, Mildura, Bendigo and Avalon airports, while police will patrol road borders.

Meanwhile health officials are contacting everyone who has flown from NSW to Victoria since December 11 and ordering those from "red zones" to get tested and self-quarantine for 14 days from the date they were last there.

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ACT Health Minister Rachel Stephen-Smith echoed the concerns of Mr Foley, warning anyone planning to visit the region in the coming few days.

She said while some Canberrans had early Christmas plans to travel to the populated area, it would be wise to "think twice" until the situation was brought under control.

"I know that's going to be difficult for a lot of people," Ms Stephen-Smith said

"If you don't need to go to Sydney this weekend, don't go - stay in Canberra.

"We are seeing that new locations are being identified as part of this cluster. We already know some people in this cluster are not necessarily located in the northern beaches.

"My advice would be really think twice if you are intending to travel to Sydney this weekend. That's not necessarily going to be our advice for the longer term or leading up to Christmas."