Victoria has shut out travellers from NSW as health authorities race to contain low levels of community coronavirus transmission.
Motorists queued up to get to Victoria before the Friday midnight deadline to avoid having to quarantine, with Melbourne Covid-19 testing centres swelling to cope with thousands of tests.
The hard border brings to an end a confusing progression of lesser border restrictions Victoria had been making since the lead-up to Christmas.
The latest cases of community transmission in Victoria are two people linked to a bayside Thai restaurant who then travelled to NSW.The pair is not yet counted in official daily numbers for Victoria.
The Victorian government sent out a statement on Friday saying the pair attended the Buffalo Smile Thai restaurant on December 21.
They travelled to Lakes Entrance a week later on December 28 and 29, then went on to Bega and Bermagui in NSW.
Victorian public health authorities contacted them on December 31, where they were already in a NSW Covid-19 testing line, a spokeswoman said. The pair is now isolating in Victoria.
Apart from these two cases revealed on Friday, another eight Victorian cases are linked to the Black Rock restaurant.
"We now have two separate groups of people who are unknown to each other who were adjacent with each other in the restaurant," Victorian testing manager Jeroen Weimar said.
A NSW returned traveller was also at that restaurant.
Health Minister Martin Foley said that was the primary line of investigation for the outbreak.
No link has been found between the eight cases and any other known infections and genomic testing is underway to confirm if the traveller is the root of the outbreak.
Mr Weimar said 170 primary contacts of those eight cases are the major concern, and hundreds of secondary contacts are also being asked to get tested and self- isolate for 14 days.
"If your primary close contact connection turns out not to have been infectious you will be released from that investigation and you are free to go," he said.
One of the positive cases recently moved to a holiday rental at Leongatha in the state's east, widening the area of close contacts.
Five exposure sites are among those authorities are most concerned about, including the Thai restaurant.
Royal Brighton Yacht Club, Holy Family Parish Catholic Church in Doveton, the clubhouse bar at Woodlands Golf Club in Mordialloc and the Village Cinema at Century City in Glen Waverley are also areas of concern.
The state is handling another nine active cases in overseas travellers who are in hotel quarantine.
Anyone arriving after the Friday midnight border closure from any part of NSW must spend a fortnight in quarantine.
Mr Weimar said anyone who is already in line for the border when the hard restriction border comes into force at 11.59pm on Friday will still be allowed to isolate at home.
But those who come after the deadline must quarantine in a hotel for 14 days.
On Thursday acting premier Jacinta Allan reintroduced the mandatory masks requirement for indoors and reduced the number of visitors allowed in Victorian homes down to 15 from 30.
Victorians can continue to return from Canberra with a permit, while more details will be announced for border communities and people who are travelling through NSW to return to Victoria. WA has reimposed strict border restrictions on Victoria.