On a wet and windy Sunday, hundreds of Palestinian flags could be seen fluttering in the breeze as protesters marched to spotlight suffering in Gaza.
Rally organiser Palestine Action Group intends to draw attention to what the United Nations has described as worsening famine conditions in Gaza, as police flagged concerns of crowd crush.
Police sought an order to prohibit the protest but Supreme Court Justice Belinda Rigg rejected the application on Saturday.
With increasing concerns for public safety, the force has since permitted protesters to walk back southbound across the bridge to the Sydney CBD after the march was initially proposed to end in North Sydney's Bradfield Park.
The bridge will remain closed to motorists for most of Sunday and the metro is out of commission with scheduled repairs.
Several Labor MPs including former NSW Labor premier and former federal foreign minister Bob Carr joined the march in defiance of Premier Chris Minns alongside multiple Greens and independent colleagues.
The premier previously warned the city would "descend into chaos" if the protest went ahead.
In a statement, Mr Carr said Australians "want the Netanyahu government's humanitarian blockade to stop, the starvation and the killing to end".
WikiLeaks founder Julian Assange joined Mr Carr at the rally.
First time protesters and friends Ian Robertson, 74, and Greg Mullins, 66, said they hoped their attendance could make a difference.
"The world's gone mad," Mr Mullins told AAP.
"I came today because I don't want my kids telling me what were you doing when this mass murder and genocide was going on," Mr Robertson added.
"It's horrific and awful, we can't bear watching it."
Acting Police Assistant Commissioner Adam Johnson earlier warned police would take swift action against anyone who sought to hijack the peaceful protest.
"That's our message all the time, whether it's a public assembly or not.
"I'm talking about anyone, I'm not talking about the actual protesters specifically, but anyone, that people are expected to obey the law."
Mr Johnson also raised safety concerns, citing the rainy conditions and the number of demonstrators.
"Crowd crush is a real thing ... but in this case, the risk is the numbers are unknown," he said.
An estimated 25,000 are believed to be on the ground in Sydney, NSW Police told AAP.
Federal Opposition leader Sussan Ley questioned the shutting down of a "critical piece of infrastructure" in Sydney.
Formerly a pro-Palestinian MP in parliament before shifting her position, Ms Ley took aim at the protest organisers and suggested the rally be moved to another location.
"I respect the right of free speech and protest, but this is taking it to another level ... the protest could happen elsewhere," Ms Ley told Sky News.
Labor backbencher Ed Husic, who has been more outspoken on ending the war on Gaza, emphasised unity.
"What we are seeing is that Australians are deeply affected by the images they are seeing out of Gaza," he told ABC TV.
"They want to send a strong message through peaceful protests to governments, both here and abroad, that the killing has got to stop, the starvation has got to end."
Several thousand protesters also marched through Melbourne to block a major CBD thoroughfare with many in the crowd banging pots and pans in a nod to mounting concerns about mass starvation in Gaza.
More than 60,000 Palestinians have been killed in the war in Gaza, according to local health authorities, while the United Nations says dozens of people have died in recent weeks due to starvation.
Israel's military campaign began after militant group Hamas attacked Israel on October 7, 2023, killing 1200 people and taking more than 251 hostages.
