The 3,000 or so residents of the blocks are being told not to leave their homes for any reason for at least five days.
At least 23 cases of infection were found on two estates in recent days.
The state of Victoria recorded 108 new cases on Saturday, its second-biggest daily increase. Australia as a whole has seen 104 coronavirus deaths.
There have been at least 8,362 infections nationwide.
Victoria State Premier Daniel Andrews said the latest figures there were a very real concern to everybody.