A state premier who opposed the tens of thousands of people who wanted to march across a major city bridge to protest the suffering in Gaza has defended his stance on the grounds of public safety.

More than 100,000 people braved the rain for a pro-Palestine protest at the Sydney Harbour Bridge and similar rallies in Melbourne and Adelaide.

Dubbed the March for Humanity by organisers, it aimed to highlight what the United Nations has described as the "worst-case scenario of famine" and the 22-month-long Israeli offensive on the blockaded enclave.

Julian Assange joined thousands of protesters who walked across the Sydney Harbour Bridge. (Flavio Brancaleone/AAP PHOTOS)

High-profile participants at the Sydney protest included Wikileaks founder Julian Assange, former Socceroos captain Craig Foster and former foreign affairs minister and NSW premier Bob Carr.

But NSW Premier Chris Minns is adamant he did not misread community sentiment in trying to stop the mass demonstration from going ahead.

"Ultimately, my job is to be on the side of public safety and ensuring people live, work and protest and enjoy a city as big as Sydney," he told reporters on Monday.

"We can't just knock out the bridge every weekend. There can be a demonstration every weekend ... no one should assume it's open season on the bridge."

Several Minns government MPs and the Sydney lord mayor took part in the march and Mr Minns struck a more conciliatory tone, praising demonstrators for the peaceful nature of the rally.

Pro-Palestine protesters have been praised for their peaceful action. (Flavio Brancaleone/AAP PHOTOS)

He also highlighted that the plight of Palestinian civilians was a massive concern to him.

Federal Labor MP Ed Husic, who has become more outspoken on Israel's military campaign in Gaza since his dumping from cabinet after the federal election, said voters had sent a strong message to politicians

"Just as some underestimated the amount of people that would turn up on the bridge, I think Australian politics has underestimated how strongly Australians feel about this issue," he told ABC radio on Monday.

"This is a moment - a wake-up call - for Australian politics.

"There was a lot of middle Australia there and that's something that can't be ignored."

NSW Police praised the behaviour of the protesters but had to force them to turn around about an hour into the march on the bridge because of the "risk of injury, due to the huge number of people taking part".

Police said no arrests were made but described the fluid mobilisation of tens of thousands of people as "perilous."

Thousands of demonstrators were directed via text messages to turn back to the CBD and later wait in place - the first recorded use of the city's emergency warning system, a police spokeswoman said.

Federal Liberal Senator David Sharma, who once served as Australia's ambassador to Israel, said the protests had made him "uncomfortable".

Protesters began their march from the eastern end of the Sydney Harbour bridge. (Dean Lewins/AAP PHOTOS)

"I don't like the idea of a major piece of infrastructure being disrupted for people to campaign about something going on overseas where Australians have very little influence," he told Sky News.

Israel's military campaign began after militant group Hamas attacked Israel on October 7, 2023, killing 1200 people and taking more than 251 hostages.

The ensuing retaliatory bombardment and blockade of Gaza have killed more than 60,000 people, according to the health authorities.

Gaza's population of 2.1 million people is projected to face high levels of acute food insecurity, including one million people who face emergency levels, according to the United Nations.

The federal government on Monday announced an additional $20 million to support aid organisations in delivering food, medical supplies and other lifesaving support in Gaza.