Victoria will enter its sixth lockdown from 8pm tonight in response to unexpected new mystery cases of Covid-19 in recent days.
Eight new cases of Covid-19 were reported in the state today, with six of those from results received on Wednesday.
The lockdown will last for seven days.
Victoria Premier Daniel Andrews said today's decision to go into another lockdown was hard to make.
"The advice to me from the experts is that if we were to wait even just a few days, there's every chance that instead of being locked down for a week, if this gets away from us then we are potentially locked down until we all get vaccinated and that's months away."
Andrews said he is doing all he can to avoid a "New South Wales-style" outbreak.
Officials are concerned about an infected teacher at a school west of Melbourne and three new cases linked to her.
The source of those infections are unknown.