Just five days ago, the state had been on a two-month streak of no community transmission.

Genomic sequencing has found Victorian cases originated from Sydney's Croydon and northern beaches clusters.

It brings to 21 the number of cases linked to Melbourne's Black Rock cluster seeded by the NSW northern beaches outbreak.

More than 22,400 test results were received on Saturday, with acting premier Jacinta Allan thanking people for their patience as there were some long waits for tests.

Testing centres have been working longer hours to meet demand from travellers returning from NSW who require mandatory testing as well as those identified as close contacts and those who have been in exposure sites.

Health Minister Martin Foley earlier acknowledged the widespread disruption created by closing Victoria's border with NSW, but made no apologies.

"Given all that we've sacrificed last year, I don't think Victorians would expect anything else from the government that wants to keep their safety and their wellbeing as its first priority," he said.

The border closed at midnight on Friday.

Now, anyone who tries to cross into Victoria with be turned back.

The only people who can freely cross from NSW to Victoria are essential workers, such as freight drivers, and border community members along the Murray River with permits.

Others must apply for an exemption via the coronavirus hotline on 1800 675 398.

Other states and territories have made increasing efforts throughout the week to protect themselves against infections from Victoria.

WA has reimposed a hard border with Victoria and other states are selectively shutting their borders to anyone who has been in the same location as a confirmed case.

Victorian exposure sites are now in: Black Rock, Brighton, Cape Schank, Cheltenham, Doveton, Forrest Hill, Fountain Gate Shopping Centre, Hallam, Glen Waverley, Lakes Entrance, Leongatha, Mentone, Mordialloc, Melbourne CBD, Moorabbin, Mount Waverley, Oakleigh, Southbank, and Wonthaggi.

Specific locations within those suburbs can be found on the Department of Health and Human Services website.

Australian Associated Press