Workers in Melbourne’s west have been urged to get tested for COVID, amid fears someone with who unwittingly has the virus is moving around the community undetected.

Acting chief health officer Professor Benjamin Cowie raised the alarm on Thursday, alerting the public to the concerning sign in wastewater test results.

“Possibly of greatest concern at the moment is the strong, repeat detections identified and reported regularly in an industrial precinct in Sunshine West,” Professor Cowie said. 

Authorities suspect the case is someone who works in the area and has not yet been tested for the virus.

“We are continuing to see a number of what we call unexpected detections of COVID-19,” he said.

“While the testing program isn’t necessarily a smoking gun, it does provide a good signal and another line of intelligence for us to follow.”

More than two-thirds of Victoria’s COVID-19 cases on Thursday were from day 13 tests, with most coming from students and close contacts of a Melbourne school.

There were 57 coronavirus cases in the community on Melbourne’s 200th day in lockdown. It was the state’s highest daily tally since the second wave.

Of those, 54 were linked to known outbreaks while 44 had been in isolation throughout their infectious period.

Premier Daniel Andrews said 41 of the 57 new local cases confirmed on Thursday were detected in isolation through routine day 13 tests.

Of the 41, 38 are students and households linked to the Al-Taqwa College outbreak and will have to restart their isolation period.

“I know 57 seems a very big number, but when the vast majority of those have been isolation for their infectious period … that’s exactly what we want,” Mr Andrews said.

Three of the new cases remain under investigation. They are in the Melbourne suburbs of Ascot Vale, Doncaster and Glenroy.

There was also a “significant uplift” in testing numbers across the state, with almost 50,000 recorded.

Mr Andrews said the isolation status of most of those cases was proof the system was working as it should.

“It goes to that point we have made a number of times that the numbers, yes they are important but the story that sits behind those numbers is in fact more important than the numbers alone,” he said.

‘Not the time to be at playgrounds’: Premier

Mr Andrews also noted that a large percentage of the 296 active cases in the state are children and young people.

“We’ve got 25-30 per cent of cases out of this outbreak are kids. When I say kids, under 10. Go out to the teenage the numbers grow,” he said.

He said playgrounds would remain closed and acknowledged that while the decision had been hard on families, it was “the right thing to protect our children”.

There are about 12,000 primary close contacts in isolation and more than 480 exposure sites in Melbourne, including daycare centres and a bank in the CBD.

• For a full list of Victoria’s exposure sites click here

The state is pursuing a vaccine target of one million doses in five weeks, and will open three new drive-through vaccination hubs.

Those will be at the Eagle Stadium at Werribee, the old Ford factory in Broadmeadows and at Sandown racecourse.

-with AAP