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Protestors in Melbourne CBD face off with riot police

A busy Melbourne freeway has been brought to a standstill for hours by more than a thousand protesters against mandatory COVID-19 vaccinations and other restrictions for the construction industry.

The demonstrators, many wearing hi-vis gear, started their second day of protests outside the CFMEU headquarters on Tuesday morning before moving on to parliament following warnings from the riot squad.

The crowd circled the city centre for hours before making their way to the West Gate freeway entrance just after 2pm, blocking traffic ahead of peak hour.

They walked to the top of the West Gate Bridge, singing, dancing and lighting a flare before turning around and heading back down the bridge about 3.30pm.

Earlier, the riot squad, supported by police on horseback, warned the group to stay back and fired what is believed to be rubber bullets into the crowd near the Queen Victoria Market.

Empty bottles and cans were thrown back at police.

The crowd then walked towards the police line with hands raised chanting "you serve us".

Empty cans of rum and cola lay strewn across the road outside parliament once the crowd had moved on from there.

Many walking with the crowd are carrying cans and bottles of alcohol, others are wearing the Australian flag as a cape, and another is carrying a Trump 2020 flag.

Most are wearing some form of hi-vis or workwear.

Flares and fireworks have been set off throughout the day and a news crew assaulted.

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The Australian Nursing and Midwifery Federation has called on city protesters to "stop thinking only of themselves, stop the violence and put the health and welfare of the Victorian community first."

"Nurses, midwives and carers are exhausted and frustrated as they watch protesters fight for their right to overwhelm our health system," secretary Lisa Fitzpatrick said in a statement.

The rally is opposing a Victorian government mandate requiring all construction workers to get vaccinated against COVID-19.

The group were chanting "f*** the jab" and "f*** off (Premier) Dan Andrews" but were blocked from accessing the CFMEU offices by a line of police officers.

"Man-baby Nazis" are being blamed for a violent protest at the CFMEU in Melbourne on Monday.

"Man-baby Nazis" are being blamed for a violent protest at the CFMEU in Melbourne on Monday.

On Monday, riot police were called in to disperse a group of about 500 protesters, who threw bottles at Victorian CFMEU construction secretary John Setka and smashed the office's door down.

Mr Setka said the protesters were not all CFMEU members and blamed "neo-Nazis and right-wing extremists" for hijacking the event.

"There was a small minority of construction workers, some of them when it all got violent just walked away from it. It was hijacked by the professional protesters," Mr Setka told ABC radio National on Tuesday morning.

He said the CFMEU was "pro-vax" but had always supported freedom of choice.

Mr Setka urged the Victorian government to tackle misinformation about COVID-19 vaccines.

He told 3AW radio he was not at the CFMEU building on Tuesday morning.

Federal member for Maribyrnong and former union leader and Bill Shorten said he believed a group of professional troublemakers were to blame for Monday's "shocking violence".

"I never thought I would see a scene where you have people who call themselves Nazis using encrypted message systems to bring in a rent-a-crowd," he told the Nine Network on Tuesday.

"Some of those people ... I'm reliably informed were fake tradies.

"There is a network of hard-right man-baby Nazis, just people who just want to cause trouble - these man-babies, they want to complain about vaccinations."

On Monday night, the state government announced the industry would be shut down from Tuesday for two weeks in metropolitan Melbourne, City of Ballarat, City of Greater Geelong, Surf Coast Shire and Mitchell Shire.

All worksites will need to demonstrate compliance with health directions before reopening.

This includes a requirement for workers to show evidence of having had at least one dose of a vaccine before they return to work on October 5.

Australian Associated Press