There was "no choice" but to shut down Victoria's construction industry due to the spread of COVID-19 and poor compliance with restrictions, the state government says.
Health Minister Martin Foley on Tuesday defended the late-night decision to close construction in locked-down Melbourne, Geelong, Ballarat, Mitchell Shire and the Surf Coast.
An official government statement announcing the blanket shutdown, effective at midnight, was not issued until 10pm on Monday.
Mr Foley said the government had for weeks warned the sector could be shut down due to outbreaks linked to the predominantly young and mobile construction workforce.
"The public health team was left with no choice but to hit the pause button and continue working with the sector over these next two weeks to improve compliance," he told reporters.
There are 337 cases directly linked to 154 construction sites, he said.
Of those 239 cases are linked to sites in metropolitan Melbourne, including nine people who live in regional Victoria.
Industrial Relations Minister Tim Pallas said inspectors visited thousands of worksites during the past week and about half were failing to comply with health directions.
"Broad-scale non-compliance across the industry was constituting a threat to public health in the most dramatic of terms," he said.
The shutdown followed a violent protest outside the CFMEU's head office in central Melbourne, but Chief Health Officer Brett Sutton said it did not trigger his decision.
He also defended his move to require all construction workers to get vaccinated against COVID-19.
"When we had a blitz offering up the vaccine for construction workers and it was voluntary, there wasn't a terrific response," he said.
"Having a mandate ... brings forward the (vaccination) coverage very substantially."
Both Mr Foley and Mr Pallas condemned Monday's violence, with the former describing it as "deplorable and an insult to every Victorian who has been doing the right thing".
The protests continued on Tuesday, with the riot squad and mounted police facing off with a hi-vis wearing crowd who marched through the city and blocked the West Gate Bridge.
The CFMEU Victorian construction branch secretary John Setka said a "small percentage" of the protesters were union members and described the scenes as "absolutely disgusting".
An amnesty will be in place on Tuesday so a limited number of workers can attend construction sites to shut them down safely.
The Property Council of Australia said the shutdown would cost the economy $1.1 billion a week.
Mr Pallas said support for the industry would be announced in the coming days.
All construction sites will need to demonstrate COVID-19 safety compliance before reopening, including proof workers have had at least one vaccine dose before returning on October 5.
Opposition Leader Matthew Guy said the Liberal-Nationals believed vaccine mandates should only apply to aged care and healthcare workers.
"There are other ways to do this and that is around education and leadership," he told reporters.
The shutdown began on the same day Victoria recorded 603 new COVID-19 cases - its highest daily tally in the current outbreak and since August 2020 - and one death.
There are 6000 active cases in the state, while this wave's death toll is 13.
Among the latest cases is an outbreak at Meadow Heights Aged Care, with 11 staff and four residents infected. Affected residents are being transferred out of the facility.
Professor Sutton said 94 per cent of the home's staff were fully vaccinated and the remainder had had their first dose, while 77 per cent of residents were fully vaccinated, some were partially inoculated, and the remainder had declined.
Australian Associated Press