Anti-war protesters set bins alight and threw horse manure at police during clashes in Australia on Wednesday, with officers arresting 33 people and using tear gas, stun grenades and pepper spray to disperse the crowd.
Activists were protesting against a three-day military expo in Melbourne which showcases weapons and technology from around the world.
Local police, fearing crowds of as many as 25,000 protesters, diverted resources from regional areas in anticipation -- making it the force's biggest operation in 20 years.
But police said only 1,200 turned up Wednesday, many of whom yelled at expo attendees before clashing with police.
"Victoria Police is appalled at the behaviour of some of the protestors in attendance at the Land Forces protest in Melbourne's CBD this morning," the state police force said in a statement.
Police said they had been "pelted" with bottles, rocks and horse manure while trying to protect expo attendees, some of whom were also assaulted by protesters.
Protesters also sprayed officers with "a liquid irritant, some of which has been identified as acid", police added.
Demonstrators set bins and wooden pallets alight and formed a make-shift barricade, according to AFP journalists.
"Whilst we respect the right for individuals to protest lawfully, we will not tolerate the behaviour of those who break the law," police said.
Activist groups -- including Extinction Rebellion and Students for Palestine -- have united for the protest, which they said was triggered by Canberra's stance on the Gaza conflict.
"We're protesting to stand up for all those who have been killed by the type of weapons on display at the convention," spokeswoman Jasmine Duff told The Age newspaper.
Police arrested 33 people and deployed tear gas, stun grenades and pepper spray to disperse the crowd.
Prime Minister Anthony Albanese said people had a right to protest, but he disagreed with violence.
"People have a right to protest peacefully, but you don't say you're opposed to defence equipment by throwing things at police.
"They've got a job to do and our police officers should be respected at all times," he said.