Midfield Group general manager Dean McKenna said the company had been given the green light to return to full operations on Thursday morning.

"We're back at work from the first shift on Thursday," he said.

"We're still waiting for some tests to come back from the testing centre.

"All the tests we've received so far have come back negative.

"The testing centre has been run off their feet with requests for tests from all over Melbourne."

Mr McKenna said the Department of Health and Human Services had approved the return to work.

"We must thank Craig Fraser and his staff at Southwest Health Care for their assistance over the last few days, plus our staff and the local community for being so supportive of us in these difficult times," he said.

On Tuesday Mr McKenna said DHHS officials were pleased with how the company handled the situation.

Close to 900 workers were tested on Monday after a decision to close the Midfield processing site late on Sunday night.

A meat inspector who visited the west Warrnambool abattoir on Tuesday last week returned a positive COVID-19 test on Sunday.

Meatworks management was on Sunday given the OK by DHHS to continue operations on Monday but the company decided to err on the side of caution for the safety of workers and the community.

All staff undertook tests on Monday through South West Healthcare.

By Tuesday evening more than 500 tests had all returned negative results.

The Warrnambool situation developed while a cluster outbreak surfaced at Colac's Australian Lamb Company abattoir.

That meatworks has been closed for a fortnight and all staff told to self isolate for 14 days.

The cluster of coronavirus cases linked to an abattoir in Colac has continued to rise, with four more recorded Wednesday afternoon.

So far 17 cases have been linked to Australian Lamb Company in Colac, up from 13 on Tuesday and there are 26 active cases in Colac Otway Shire.

An abattoir worker returned a positive test on July 10.

That led to a positive test of a student at Trinity College and now 70 per cent of students are staying home from school.

With some Hampden league junior players attending Trinity College, games at Camperdown and Cobden were called off last Saturday.

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