The tests results confirmed are family contacts. The confirmation came after two of the positive cases were detected in Melbourne's northern suburbs on Monday morning.

Health minister Martin Foley confirmed the cases in a press conference on Monday afternoon.

"This morning, the Department of Health was advised of two positive cases of COVID-19 and Melbourne's northern suburbs," he said. "Both of whom reside in the city of Whittlesea.

"Case one went to the centre for testing on May 23 due to the symptoms he was experiencing which he had, it would appear, from May 20 onwards.

"He was joined at the testing centre by case number two, a male relative who was asymptomatic.

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"We put public health actions in place, including isolating and testing of all of those family members.

"As a result of those tests, a further two positive tests among those family members have been identified; case three, a woman, and case four, a child."

Mr Foley said other family members of the cases returned negative COVID-19 tests.

"Today, our public health teams have been investigating the situation and continue to interview and test all of the individuals and their contacts," he said.

"The contacts of contacts will begin to ramp out over coming hours and days. I can advise that one of the individuals lives within the wastewater catchment areas that produce the strong detection that we reported last Friday.

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"There is, as yet, no indication that these individuals are linked to any exposure sites from the previous alert case."

People who have been to the following sites in these timeframes are required to immediately isolate, get tested and quarantine for 14 days:

People can view current exposure sites at coronavirus.vic.gov.au.

"I urge all Victorians to be cautious because we are coming into winter, the highest risk period of transmission in our community," Mr Foley said.