There have been extraordinary scenes outside union offices in Melbourne as construction workers flew into violent rages against mandatory vaccination rules for their industry.

Glass bottles were pelted at the Melbourne headquarters of the CFMEU as the protest turned ugly, with the union blaming “outside extremists” for the violence.

Just before 4pm, the bottles were thrown at the already smashed glass entrance doors to the building in Melbourne’s CBD as those protecting the entry sought refuge indoors.

About the same time, there were reports that police had surrounded the union building, with protesters trapped inside their lines.

Hundreds of construction workers rallied throughout most of Monday in opposition to having to show proof of a COVID vaccination to be allowed back on building sites, with some saying they would rather the entire industry be shut down.

There is a 25 per cent cap on the industry’s workforce in Victoria, with tradies required to have had their first dose of a vaccine by this Thursday to be allowed back to work.

Watch the violence here (warning: Explicit language)

Tweet from @suzandelibasic

Monday’s protest escalated when two union officials, including Victorian construction branch secretary John Setka, came outside the Elizabeth Street office to speak to protesters.

Mr Setka was met with boos and insults from the crowd, while some protesters hurled bottles and even bread crates.

“Please calm down, can you at least give me the respect to talk. We’re not the enemy, I don’t know what you have heard,” he says to protesters, in a video posted to social media.

“I have never ever said I support mandatory vaccination.”

The protesters then called for the CFMEU leader to “stand up or stand down” and yelled “we are one”.

Once Mr Setka went back inside, the protesters smashed the building’s glass door.

By 1pm the protest had swelled to fill both sides of Elizabeth Street, with union delegates standing out the front of the building to stop protesters from entering.

Some protesters called for Mr Setka to come outside and march with them, saying they would come to the CFMEU office every day until the union bowed to their demands.

Police are gathered around the rally and have blocked off parts of the road, but do not appear to be moving on protesters.

It was unclear whether all of those protesting are construction workers, with a message on the Melbourne Freedom Rally Telegram group encouraging anti-lockdown protesters to join them.

“If you are in the area and wish to support these guys head down,” a Telegram message said.

Another said: “If you got a high vis just get down there NUMBERS!”.

Tweet from @edengillespie

Later Mr Setka said he was “quite disappointed” with the violent protest.

“All we have ever tried to do is keep our industry working safely,” he told Melbourne’s 3AW radio.

Earlier, Premier Daniel Andrews said during his daily coronavirus update that the protest was “not smart, they are not safe”.

“This industry is open at 25 per cent, we want to get to 50, being vaccinated is an incredibly important part of that,” he said.

“Protests don’t work. Getting vaccinated works, following the rules works, that’s how you stay open, that’s how you get open.”

Victoria posted an outbreak high of 567 local COVID cases on Monday. The death of a woman in her 70s took its toll from the current outbreak to 12.

At least 20 of Monday’s cases were linked to construction sites. Victorian COVID commander Jeroen Weimar said the number of sites and workers travelling between Melbourne and regional areas were major concerns.

“We know this is a difficult and complex time but we can see from the pattern of cases we have seen over the past week or two and its exposure to Ballarat, to Geelong, to Mitchell Shire, that we need to minimise movement across the construction industry,” he said.

Last week, concerned at the spread of the virus on large construction sites, Victorian authorities banned workers crossing the Melbourne/regional divide. Government worksites are exempt from the ban.

It also mandated vaccines for everyone on construction worksites – and the number of workers on site can return to 50 per cent once vaccination rates hit 90 per cent.

Site tearooms, where numerous virus cases have been picked up, have also been closed.

Those changes brought construction workers out onto Melbourne streets on Friday for sit-down smoko and lunchtime protests that blocked CBD streets.

-with AAP