Jeroen Weimar said the state is monitoring wastewater from NSW local government areas along the border.

He said Victorians in regional NSW should already be coming home.

"You need to come home now, chances are in the coming hours or days we will be forced to upgrade NSW to red or close the border, that is a significant likelihood this point in time," he said.

The dire statements came as NSW recorded 50 new cases of COVID, of which 37 were in the community while infectious.

Mr Weimar said there would not be any more warnings to Victorians and any closure would be immediate.

"If the situation gets to the point where it's beyond critical [NSW] will go red and we will enforce those border requirements," he said.

More than 300 Victoria Police officers are undertaking spot checks and monitoring the state's border.

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Mr Weimar said the situation in Sydney was on a razor's edge and officials were monitoring it hour-by-hour.

"We have no wish to extend any further actions but when you've got over 500 cases in the greater Sydney area that's a very high viral load, that's the largest outbreak seen anywhere in Australia this year," he said.

Mr Weimar said he had no imminent announcement to make on the closure.

"There is no imminent announcement right now at this moment but we are exceptionally concerned about the NSW situation," he said.

"I would not be surprised if we were in a position where we felt we had to extend the red zone beyond Greater Sydney area, we already have significant border checks and border patrol in place through out colleagues in VicPol."