Protesters were pepper sprayed, arrested, beaten and shoved by police as they gathered at Sydney Town Hall to speak out against Isaac Herzog, who arrived in the harbour city on Monday.
Organisers had hoped to march through the city but a court decision, that upheld the police's ability to restrict protests, scuppered plans.
As the demonstration drew to an end, the group moved towards the exit, with some trying to leave and others calling on the hundreds of surrounding police to let them march.
Though there was an exit towards the south side of the block where some could trickle out, along most of the square's mouth, police restricted movement and would not let people march, forcing the large group into a gridlock.
Protesters' chants soon grew louder and the police presence swelled.
Officers issued a move-on order but many within the immense, densely packed crowd of roughly 5000 were unclear on directions and the situation quickly devolved.
Police on foot and on horseback formed a front and rushed at the protesters as they attempted to disperse the group.
Others were seen beating and deploying pepper spray at attendees, and at one point a group of Muslim men leading a prayer were ripped from their knees and taken away by police.
Media, including photographers and those with press passes displayed, were forcibly pushed away from the scene by officers.
The streets were lined with medics kneeling over pepper-sprayed protesters, pouring water into their eyes as they sputtered and hacked up phlegm.
"Instead of respecting the right of 50,000 people who turned up to express their outrage against our government celebrating someone accused of inciting genocide, the police resorted to unleashing unseen violent repression," Palestine Action Group Sydney wrote in a social media post.
The NSW police union defended its members' response, saying their actions were proportionate.
Police said 27 people were arrested, including 10 for assaulting officers.
NSW Police assistant commissioner Peter McKenna said the protesters' behaviour was outrageous.
"It was outrageous, the behaviour," Mr McKenna told the media on Monday night.
"We saw officers being threatened, jostled and assaulted."
Prior to the chaos, the crowd stood peacefully and chanted in between speeches from people such as former Australian of the Year Grace Tame, Jewish academic Antony Loewenstein, and Amnesty International Australia spokesman Mohamed Duar.
Protests across other major Australian cities also drew strong attendance as participants spoke out against Israel's bombardment and starvation of Gaza - which has killed more than 70,000 Palestinians - and decried photos of Mr Herzog signing an artillery shell that would be dropped on the occupied territory.
Mr Herzog was invited to Australia by Prime Minister Anthony Albanese after the Bondi mass shooting in mid-December.
He visited the scene of the terror attack on Monday and is set to attend more community events on Tuesday.
Asked by AAP if he had a message to protesters, he claimed the demonstrations "undermine and delegitimise" Israel's existence.
He previously said Palestinians bore collective blame for Hamas' attack on Israel on October 7, 2023, before later walking back the remarks.
A United Nations Human Rights Council commission of inquiry in September found the statement might reasonably have been interpreted as inciting genocide.
The Australian government has said Mr Herzog's visit would provide comfort to the Jewish community.
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