Victoria has recorded another four Covid-19 infections bringing the Melbourne cluster to nine.
The government here has suspended the quarantine travel bubble with Victoria for at least 72 hours.
Melbourne is also bringing back some restrictions - including mandatory face masks and limits to gatherings.
The four new cases confirmed this afternoon are all family contacts of the most recent case - a man in his 60s.
University of Melbourne epidemiologist Professor Tony Blakely told Checkpoint the new Covid-19 cases in Melbourne were probably contracted from the fifth case a week ago.
Professor Blakely told Checkpoint: "Things have changed dramatically in the last 90 minutes with these extra four cases.
"These four cases are parallel, if you like, with the case that was found this morning.
"They're all in the same household so that makes you feel a bit confident, but the downside here is that this person - the fifth case this morning - actually probably passed it on to most recent cases a week ago.
"We have a problem on our hands" if these latest four cases have been moving around the community with the virus in the last week," he said.
"We don't yet know that. That type of information will be worked through right now... But it does become somewhat more concerning, the situation in Melbourne."
