Mr Andrews said a hard border would come into effect at midnight on Thursday and would last for 48 hours.

Under the restrictions, only people with medical emergency needs, urgent animal welfare, or freight drivers would be able to cross the border.

Mr Andrews said after the two days, a permit system would come into place.

Mr Andrews said he had been working with local councils near the border to help navigate the new rules.

"That is about making sure we have a clear picture and we can take action to support those communities in the event they need fuel, food, medical supplies," he said.

"Those border communities have done it tough for a long time - for pretty much the whole year.

"We're not looking to make things more difficult. In fact, we'll provide any and all support we can to those communities."

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The final details of the permit scheme are still forthcoming.

Reasons to enter Victoria from South Australia include emergency services worker or a worker providing essential services, for agricultural work, to receive medical care (including seeking coronavirus testing), obtain medical supplies or compassionate reasons, and to shop to obtain essential supplies.

Mr Andrews said the border restrictions would be in place "no longer than they need to be."

"It is important we work with South Australia to get the border back open as soon as possible," he said.

The two states had only recently come to an agreement to reopen the borders from December 1, with Victoria exiting its second wave of COVID-19.

South Australia recorded zero new COVID-19 cases on Thursday and has a total of 23 active cases.

The state entered the harshest lockdown Australia had seen on Thursday for six days.

Mr Andrews said all truck drivers crossing from South Australia would also be tested.

A testing site was set up near Nhill and began testing on Thursday.

Mr Andrews said drivers who refused a test would be turned around.

It comes after "fragments of the virus" were detected in untreated wastewater near Portland and Benalla on November 17.

Anyone who visited those areas and has developed COVID-symptoms was encouraged to get tested and isolate.

As SA deals with its outbreak crisis, Victoria reached 20 consecutive days without any deaths or new cases on Thursday.

South Australian Chief Public Health Officer Nicola Spurrier said she hoped South Australia could be back open by Christmas.

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