Victoria will start 2021 by closing its border with NSW as it battles a fresh coronavirus outbreak.
Twelve months after the state ushered in the new year battling devastating bushfires, authorities are moving to contain a cluster that has grown to eight cases and more than 70 close contacts.
The border closure comes just over a month after NSW had reopened its border with Victoria, which had been shut since July.
Announcing the measure at a snap media conference on Thursday afternoon, acting Premier Jacinta Allan acknowledged that the closure would affect "thousands, possibly tens of thousands" of Victorians who are in NSW.
The hard border will start from 11.59pm on January 1.
Anyone who arrives back in Victoria from anywhere in NSW from midnight on Thursday will have to be tested and go into isolation for 14 days.
While Ms Allan apologised for the border closure, she made it clear Victorians who are in NSW should not surprised.
"We have been sending a very strong message for the better part of a week-and-a-half, 10 days now, advising people to think very carefully about their travel to NSW," she said.
"These difficult decisions are about protecting the community, protecting and keeping case numbers low and doing everything we can to lock in the gains we have made over the course of 2020."
Masks will be mandatory indoors from 5pm on Thursday and the number of visitors allowed in Victorian homes is down to 15 from 30 under changes announced by Ms Allan earlier in the day.
She also announced two additional cases identified on Thursday afternoon and these are close contacts of the six previously announced.
These cases, which first emerged on Wednesday night, ended a 60-day streak without infections for Victoria.
It's believed all six cases - including two women in their 40s and a woman in her 70s - are tied to outbreaks of the virus in Sydney.
All are directly or indirectly linked to the Smile Buffalo Thai restaurant in Black Rock on December 21, which was attended by a NSW returned traveller.
That traveller returned before border permits were in place and was being tested on Thursday.
Victoria's testing chief Jeroen Weimar said early information indicated a potential exposure window between December 17 and 19.
Earlier on Thursday Health Minister Martin Foley urged Victorians not to travel to NSW and for any Victorians in the previous NSW green zone to return immediately.
"You do not want to be caught on the wrong side of a rapidly evolving situation," he said.
The new Black Rock exposure site is on top of a series of locations released by the health department late on Wednesday, with exposure dates between Boxing Day and December 28.
They include Katlialo restaurant in Eaton Mall in Oakleigh; Mentone/Parkdale Beach; Century City Walk and Mocha Jo's in Glen Waverley; Kmart, Big W Target, Millers, King of Gifts and Lo Costa stores at the Fountain Gate Shopping Centre, and the Holy Family Catholic church at Doveton.
The National Golf Club is another exposure site, while the Royal Brighton Yacht Club announced it had closed for deep cleaning after a positive case dined in its restaurant outdoor area on December 29.
Anyone already in Victoria who travelled to those locations since December 27 should be tested and stay at home until their results come back.
Victorians can continue to return from Canberra with a green zone permit, while more details will be announced for border communities and people who are travelling through NSW to return to Victoria.
Opposition Leader Michael O'Brien said Victorians shouldn't panic and new cases were inevitable.
"What's really important is we keep in place the measures to keep us safe," he said, supporting the latest restrictions.
Celebrations for the Victorian new year were already going to be muted on Thursday night, with Melbourne's fireworks display cancelled weeks ago.
Meanwhile, a 57-year-old NSW woman was arrested after speeding through a checkpoint in East Gippsland on Wednesday, coming from a designated red zone.