Melbourne protester Daniel said he had been supportive of the Palestinian cause since his university days in the 1990s. 

"It makes me really, really sad that three decades later, we're still fighting for this," he said.

"As a father now, I'm moved even more than I was ... because I can see the faces of my children in the starving faces of those children in Palestine.

"I think it's starting to break the hearts of a lot of Australians. We take a lot for granted in this beautiful country ... that we have here, but there comes a time we have to get out and let your voice be heard and send a message."

Another protester, Li Mei, said she it was a "really important time" for the Australian government to recognise Palestine as a state.

"I think we could have a chance in ending this war if everyone stands up and continues to stand up for Palestine and for all the suffering that Israel has caused," she said.

"I just want the war to stop."

Acting Deputy Commissioner Peter McKenna has emphasised to reporters that NSW Police "are not anti-protest".

He says police facilitate more than 1,500 protests in Sydney every year.

"Our whole issue today was never about the fact that they are protesting," he says.

"Today was all about public safety for us and having the time to plan out a proper protest where we take safety into consideration.

"Quite clearly today showed us that we had to scramble. We had to make snap decisions.

"It came very close to us having almost a catastrophic situation."

NSW Police Acting Deputy Commissioner Peter McKenna has just been asked if police would "resist again" if protesters marched on the Sydney Harbour Bridge in the future.

He says it's "not about resisting or not resisting".

"It's certainly about assessing a Form 1 (protest permit) on its own merits, assessing the public safety aspects of the Form 1, what they want to achieve, how we go about it," he says.

"And we do that each and every time on its own merits.

"What I would say if we get a Form 1, giving us seven days notice, I can tell you now, after what happened today, certainly I would have grave concerns about allowing it to go."

Craig Moran, the Executive Director of Transport for NSW's Operations Management has now told reporters that the march through the CBD caused "quite a bit of congestion" among motorists impacted by the protest.

"I'd like to say is just to thank the people of Sydney who took the advice to avoid the area to avoid non-essential travel," he says.

"There was quite a bit of congestion, particularly on the road network and the Anzac Bridge when the initial closure was put in place.

"We saw massive crowds that we had to work with police to manage. 

"We equally had concerns about how we could safely accommodate those numbers, particularly at North Sydney station, and really supported the need to get them back towards the CBD, where we had more options to help get them home."

The NSW Police Acting Assistant Commissioner and Central Metropolitan Region Commander Adam Johnson is now speaking.

He says that in his 35-year tenure as a police officer, he has never seen as "perilous" a situation as the march through Sydney today.

"I was honestly worried that we were going to have a major incident with potential loss of life," he has told reporters in Surry Hills.

"I just want to shout out to all of the police on the ground, the police that were working with me, the decisions we made on the run critically and quickly, and particularly the messaging we got together.

"I think went a long way to averting that."

We're now hearing from the NSW Police Acting Deputy Commissioner Peter McKenna.

He says that the NSW Police have estimated that "around 90,000 people" attended today's march across the Sydney Harbour Bridge.

"Make no mistake, public safety was a real concern to us today," the acting deputy commissioner says.

"Whilst those numbers were far greater than what the organisers asked for… I'm really happy that the police on the ground, the police commander ran an operation today where they had to make very big decisions very quickly to ensure people's safety.

"At points today we were really concerned about a crowd crush.

"We could not allow those numbers to then egress into the northern side, into those train stations without again, that real risk of crowd crush. 

"Speaking to some of the people who were on the bridge whilst they were well behaved, it did cause some confusion. 

"There were people still trying to move north, others stopping and then we told people that we wanted them to move south and we had to do that incrementally. 

"Again, that was some confusion with people on the bridge and at points there, we were worried that they were going to come together. 

"So, this operation, from our point of view, was a success in that no one was hurt, no people were hurt, no police were hurt."

The harbour bridge has been cleared of protesters and has reopened, five-and-a-half after it closed this morning.

It was initially scheduled to be operational for motorists by about 4pm.

One Melbourne protester, who told the ABC she was a nurse, said she had been attending the protests regularly since the Israel-Gaza war began.

"We don't see that hospitals and children and nurses and healthcare workers should be a target," she said.

"Our coworkers in Palestine have been murdered, it just has to stop."

Israel has faced criticism from human rights groups for launching strikes on hospitals during the war, which are meant to be protected under international humanitarian law. 

The nation has claimed hospitals struck were being used by Hamas for military purposes.

Another protester, Zeina, said she was "sick and tired of seeing emaciated children on my screen every single day".

"Children dying, children being bombed, women crying for their dead children," she said.

"Fathers looking for bread and being shot when they're just trying to get basic needs for their children ... it's not ok."

Now that protesters have been cleared from the Sydney Harbour Bridge, here's another angle of the march that shows just how many people were in attendance.

Witness footage popped up online earlier, filmed from the window of a passing train that was travelling over the bridge as people were walking.

The NSW Police have shared an insight into how they kept a close eye on all of the events of today's Sydney Harbour Bridge march.

Images have been released from inside the Police Operations Centre, which was tasked with managing the crowd as protesters made their way across the harbour bridge.