ACT Health Minister Rachel Stephen-Smith said from 6pm Tuesday, anyone who had been in greater Melbourne in the past 14-days must complete an online declaration form in 24 hours from the time it was available.

She discouraged travel to the Victorian capital after five new COVID-19 cases were reported in the past two days.

"At this point, I probably wouldn't go to Melbourne just until we see what happens next," Ms Stephen-Smith said.

"That's not because necessarily the risk of continuing transmission in the community is considered to be particularly high at this point ... but probably more for people's consideration, there is a risk that then additional requirements will be put on people who've returned from Melbourne.

"If you are considering travelling to Melbourne ... be really conscious of the fact that you will have to complete a declaration."

Acting Victorian Premier James Merlino announced new restrictions would come into place in Melbourne from Tuesday night after a man in his 60s became the fifth person to test positive to COVID-19.

Mr Merlino said the man had symptoms prior to the four cases identified on Monday, suggesting he could be the possible "source case" for the City of Whittlesea outbreak.

The Victorian Department of Health confirmed another four new cases had been identified on Tuesday afternoon.

The department said the cases were all family contacts of the infected man announced on Tuesday morning.

There are now nine cases linked to the outbreak.

On Monday night, ACT Health advised any non-ACT residents who have been to close contact exposure sites identified in Melbourne's northern suburbs could not enter the territory without an exemption.

Ms Stephen-Smith said Canberrans were free to return to the ACT from Melbourne but they must complete the declaration form within 24 hours prior to travelling.

"The reason that we ask people to complete a declaration is so that we can get in touch with people quickly if the situation does change if we need people to do something different," she said.

ACT Health also advised staff, visitors and volunteers at high-risk areas including hospitals, aged care and the prison, should not attend work if they have been in Melbourne in the past 14 days.

"These high-risk settings include hospitals, residential aged care facilities, correctional facilities and residential accommodation facilities that support people who require frequent, close personal care and who are vulnerable to severe disease," ACT Health said in a statement.

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"Further, staff returning from greater Melbourne who provide home-based aged care and disability services that involve close physical contact with clients, should exclude themselves from providing in-home care for a period of 14 days since they were last in the area."

ACT Health said anyone who had been in Melbourne should be alert and regularly check updated exposure sites and get tested if they had mild symptoms.

People who had been to a close contact exposure site must get tested and quarantine for 14 days from the the day they were there regardless of a negative result.

Anyone who has attended a casual exposure site must get tested and isolate until they get a negative result.

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