Victoria's border with New South Wales slammed shut at midnight, barring entry to anyone who didn't make it there in time.
Vehicles arriving at border checkpoints after the deadline were turned around by police and instructed to return to NSW.
Yesterday Jeroen Weimar, the Victorian Health Department's Covid-19 response commander, justified the state's hardline stance.
"We need to close the border, because we do not wish to continue to import high-risk Covid cases back into Victoria," Weimar said.
"We do not think that would be right or fair for the Victorian community.
"We do not have the capacity to put hundreds of people into hotel quarantine because they elected to come home late.
"If there are people who've gone to NSW, we did not design and set up a hotel quarantine system to enable people who've gone on holidays in NSW to come back a bit later."
However, some people rushing to the border last night had travelled from as far away as Queensland.
Images posted on social media showed massive queues hours before the border closed.
Photographer Simon Dallinger was at the Hume Freeway checkpoint. He reported that the last people allowed through, seconds before midnight, were Kelli Rippon and Rachel Bartlett. The pair had travelled from Brisbane to Dubbo, and then to Victoria.
They made it just in time. Others were not so lucky.
Health authorities in Victoria believe the virus has been spreading there for almost two weeks.
All 10 cases reported since Wednesday either dined at the Smile Buffalo Thai restaurant in Black Rock on December 21, or are close contacts of others who did.
"We know we have a likely starting point to December 21 – that is now at 10 or 11 days ago," Weimar said yesterday.
"That gives us great reason for concern that this may cause other chains of transmission to go back to that point."
Across the border in NSW, three new infections were identified in Western Sydney yesterday.
Contact tracers are now scrambling to link the new cases to existing clusters.
Premier Gladys Berejiklian has warned tighter restrictions could be introduced across Greater Sydney if more cases arise without known links.
"If we get to a stage, or if we feel that there's too many cases that are completely unlinked or unrelated, or something pops out unexpectedly that does cause concern, then of course we'll adjust our settings if that's the case," Berejiklian said yesterday.
Today residents on the northern beaches will learn whether their localised restrictions will be loosened. The lower northern beaches, in particular, may be brought under the same rules as the rest of Sydney.