Acting Premier James Merlino has announced changes this morning, as the cluster in Melbourne grows to five.

This new case is a male in his 60s who is being linked to the existing Whittlesea outbreak.

"He reports being symptomatic before case one developed symptoms, meaning this could be a possible source case, but of course a full investigation is underway," Mr Merlino said.

"This case, like the four that we announced yesterday, have not identified any link to any of the exposure sites to the Wollert case two weeks ago.

"Genomic sequencing for this outbreak has been completed and it is closely linked to the Wollert outbreak which originated in South Australian hotel quarantine."

Changes related to regional Victoria:

Victorians visiting regional Victoria from Melbourne will also need to wear a face mask when indoors even when outside of metro areas unless an exemption applies.

Victorians who live in Greater Melbourne and need to travel to regional Victoria can still do so, however the restrictions travel with them.

There are not changes to density limits in hospitality statewide.

For Greater Melbourne:

From 6pm tonight, private gatherings in the home will be limited to five visitors per day and public gatherings will be limited to 30 people.

Face masks will need to be worn indoors, unless an exemption applies. The face mask requirement applies everyone aged 12 years and older.

The Public Health Advisory Panel will provide advice as soon as possible to upcoming Tier 1 and Tier 2 events if any modifications will be required for the event to proceed.

Schools and workplaces will remain open with the current restrictions that are in place.

Events such as weddings will not be reduced in size or activities affected, but attendees must wear masks as per previous indoor mask-wearing rules.

See the exposure sites at coronavirus.vic.gov.au which include the Highpoint Shopping Centre in Maribyrnong.

Chief Health Officer Brett Sutton said it was the Indian variant of the virus being investigated.

"We're searching across the board for all exposure sites," he said.

"We know that doing what we need to do now will save us in the long-run.

"The easiest measure is wearing a mask.

"We just need to see through all of these interviews what exposures sites there are ... and go from there."

Mr Sutton said "he wouldn't stand in the way" of other jurisdictions imposing travel restrictions on Victorians but suggested an orange or red zone designation might be appropriate.

More to come.