Masks will now be required in all indoor venues outside the home for Victorians over the age of eight in a bid to halt the state’s soaring number of Covid-19 cases.
It comes after Victoria reported 2005 new coronavirus cases and 10 deaths, marking the state's highest daily infection figure since October 22.
Acting Premier James Merlino has announced the indoor mask mandate will be expanded in hospitality and office settings from 11.59pm on Thursday.
Face masks will also be required at all major events with more than 30,000 attendees.
Mr Merlino said the move was "really critical".
"This is a sensible response which will allow businesses to stay open, bars and restaurants to continue to stay open and major events to go ahead," Mr Merlino said.
"Masks are a cheap and effective way to maintain the health of the community — it's something public health experts have been calling for."
He also urged people to work from home and gather with people outdoors if they can.
"If you can open doors and windows wherever possible if you are meeting indoors, please do," he said.
Mr Merlino said a lockdown was not considered as an option because Victoria was in a strong position due to its high rates of vaccination.
Why a mask mandate was needed
Victoria's Chief Health Officer Brett Sutton added that when a mask mandate is in place, the level of compliance is much higher.
"We usually get about 50 per cent levels of cooperation or compliance with a strong recommendation. It goes to 95 - 99 per cent with a mandate. Why would you introduce a half measure when you need the full measure to be in place?" he said.
The Victorian government had flagged it would relax mask requirements last week but instead kept mandates in retail settings, for hospitality workers and on public transport, citing the spread of the Omicron variant.
Meanwhile, Victoria's Covid testing system continues to strain under the weight of holidaymakers seeking a swab for interstate travel, with at least 20 sites across Melbourne temporarily closed as of 9am after reaching capacity.
Scott Morrison "highly recommended" wearing masks indoors and other places where social distancing is difficult after Wednesday's national cabinet meeting.
The PM was slammed by viewers after he compared making wearing masks mandatory to having to mandate people to wear sunscreen and hats in summer.
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