Health officials say they remain "very, very vigilant" when it comes to testing for coronavirus, despite the number of active cases across the state dropping to four.

Two people are being treated in hospital for the virus.

The Department of Health and Human Services' Jeroen Weimar said testing did detect what was described as a "mild positive case" in a person who had traveled to Victoria from Western Australia.

But it was not classed as a new active case, Mr Weimar said, because the person previously contracted the virus before going into isolation in WA and there was no threat to the wider community in Victoria.

Mr Weimar also indicated that masks will remain in use in Victoria, saying they were a "critical element" in the preservation of the progress made so far.

"We know it's a really important part of our armory to control coronavirus," he said.

Other news

Earlier

ZERO new COVID-19 cases have been reported in Victoria, for the 10th day in a row.

There are four active cases, newly released Department of Health and Human Services data shows.

None are in central Victoria.

Other news:

There are two cases with unknown source.

There were 10,653 COVID-19 test results received in the past 24 hours.

It comes as authorities reopen the border between regional Victoria and metropolitan Melbourne, reversing closures in place since July.

It is among several restrictions eased overnight on Sunday.

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