From 11.59pm on Sunday night, if people from those areas - tagged as "red zones" - who are not Victorians enter the state, they will face 14 days of mandatory hotel quarantine.

Victorians heading home have until midnight on Monday to return and be able to serve their quarantine period at their homes.

"The rest of NSW remains a green zone," Victorian Premier Daniel Andrews said.

"While there is a concentration of those cases in the Northern Beaches local government area, there is transmission beyond that part of Sydney and there are a number of significant exposure sites where infectious people have been in the Sydney CBD."

The news follows Western Australia reintroducing its hard border with NSW and Queensland banning visitors from the Northern Beaches local government area.

11.30am: Another 30 cases of COVID-19 from the Northern Beaches cluster has seen NSW Premier Gladys Berejiklian further tighten restrictions for the Illawarra and elsewhere in the days before Christmas.

On Saturday, Ms Berejiklian announced the Northern Beaches would go into lockdown from 5pm Saturday until midnight on Wednesday, after 23 new cases recorded in the 24 hours to 8pm on Friday night, including 10 cases already announced on Friday.

Sunday's 30 cases saw wider restrictions brought into place including a reintroduction of the maximum limit of 10 guests in homes of those living in Greater Sydney, which included the Illawarra-Shoalhaven, Blue Mountains and the Central Coast, until midnight on Wednesday.

Also, all indoor venues in these areas that their capacity restrictions eased to two-square-metres per person will have to go back to the four-square-metre rule until midnight on Wednesday.

All indoor venues will have a cap of 300 people.

Singing and chanting at indoor venues will not be allowed and dancefloors will not be permitted, except for weddings, when a maximum of 20 from the bridal party will be permitted.

"Even though numbers are higher than yesterday, the one positive is we still have not seen evidence of massive seeding outside the Northern Beaches community," Ms Berejiklian said.

People in the Greater Sydney area and the Central Coast, Illawarra-Shoalhaven, and Nepean Blue Mountains, are also asked not to visit aged care facilities until 11.59pm on Wednesday, unless it is critical.

Meanwhile, Health Minister Brad Hazzard recommended people across Greater Sydney wear masks over the coming days.

"Certainly I'm asking, and the government is asking, all residents of the Greater Sydney area to wear masks at least until Wednesday," Mr Hazzard said.

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