The Civic Park event was one of about 100 held around the country on Friday and coincided with similar events taking place in about 150 countries around the world.

Organisers of the rally said before the event they were hoping for broader community participation and that's what they got with thousands of adults turning out in support of the students.

The event, the fourth held in the city, began at about midday with a mass of people gathering in the centre of Civic Park for a series of passionate speeches from local high school students.

After 30 minutes, multiple police vehicles led a march in a westerly direction along King Street, before the crowd hooked its way through Cooks Hill and back down Darby Street to the park.

Event spokesperson Alexa Stuart said the organising team had been blown away by the level of support.

"It is so much more and so much better than any of us ever expected," she said.

"I think it really just shows the power of the people and it is so inspiring to see all of our hard work has paid off.

"There is grandparents, parents, young kids, babies, there is everyone that has come here and we're all so excited. It is such an amazing feeling."

Prior to the walk, Ms Stuart was one of a handful of speakers. The 15-year-old Lambton High School student read a speech, which doubled as a letter to Australian Prime Minister Scott Morrison, reiterating the strike action's collective message and demanding the government tackle climate issues facing the world.

"Thousands here in Newcastle and over a million around the world have come to tell you, Mr Prime Minister, that no longer will we stand for your denial, no longer will we stand for your empty words, and no longer will we stand for your total inaction on the biggest threat humanity has ever faced," she told the crowd.

Ms Stuart said if Mr Morrison really believed in a "fair go for all Australians", including the younger generations, he would listen to the three main demands of the strike movement.

School Strike 4 Climate wants no new coal, oil or gas projects; 100 per cent renewable energy generation and exports by 2030; and funds for a "just transition" for all fossil-fuel communities.

While the demands may fail to resonate with the Hunter communities whose economies are largely based on and propped up by coal mining, the rally's speakers said their actions were not an "us against you" scenario in terms of resources workers.

"We do stand with those who work in the mining industry ... this is not about us versus them. This not about the environment versus jobs ... our frustration and anger about climate inaction is never directed at coal workers, but at the people like you, Mr Prime Minister, who are failing to bring us together to create solutions that don't leave any of us behind," Ms Stuart said.

Merewether High School student Aleeyah Clifford, 17, and Lambton High School's Abby Manning, 16 spoke for the majority of the time before the walk. Their feverish words ripped the crowd into chants, boos or applause depending on the message.

For those involved in the strike, the duo's discourse appeared to be inspiring. For anyone else in the park, or walking past it, it could have been a little confronting.

"At the age of 16 I should not be fearful for my future," one of the girls said. "I should not have to think of the lives of my [future] children and whether they will survive through the coming decades.

"People right now are in danger and we are here to stop it, we are here to demand action now."

West Wallsend High's Kalleb Pritchard, 16, and Hunter Valley Grammar's Angie Devorsine, 16, also gave passionate speeches.

"Please wake up! There is no planet B," they said.

"Climate change endangers the future of humanity ... adults have ignored this issue for far too long ... our future is being taken away."

The speakers told of a string of climate-related issues around the world, including fires in the Amazon, drought in India, heat records being broken in multiple countries in Europe and extreme flooding in America.

They also referenced the erosion issues at Stockton and the dangers of seismic testing off the Hunter coast.

The recent decision to deny approval of the planned Bylong Valley coal mine was also a hot topic and viewed as a success of ongoing climate activism in Australia.

"The refusal of the mine was a massive step for us," Ms Stuart said. "I think we realised our message is really starting to get out."

Friday's strike was the first adults had been officially invited to, and thousands attended to join the action.

Scott Alcorn, 62, said he had come in from the Hunter Valley to take part as "the case for change, for action, is more and more urgent".

Mr Alcorn made a replica bulk carrier for the event, naming the coal ship the "Joel Fitzgibbon". He said he had coined the name after the Hunter MP's perceived swing back to supporting the coal industry after the federal election in May. Mr Fitzgibbon attended the Cessnock climate rally on Friday.

"He was really quiet before the election about his fascination with coal, but as soon as he looked like he was going to get dumped by the One Nation [candidate], all of a sudden he was, 'coal is the answer to all our woes'," Mr Alcorn said.

The retiree added: "one of the things that is not understood by the naysayers and detractors, is the students aren't calling for an immediate end to coal mining. They want a just transition between the folks that work in coal now into some other, hopefully, prosperous business and enterprise."

Wallsend 75-year-old Beth Moran said support for the student strikes was growing among seniors.

"It's so important for people my age," she said. "I feel a responsibility for what we've done to the earth. These young people standing up for what they believe in, they deserve to be supported and I take my hat off to them. It's not easy for them to leave school. There will be a lot of people saying 'you shouldn't be doing that, you should be in class', but I think they're doing the right thing. If they don't do it now, it's going to be too late for them."

The peaceful march was a sight to see for stunned diners on Darby Street unaware the strike was taking place. Many stood from their chairs and applauded the passing chanters, while others appeared unmoved from the food on their plates.

Merewether's Con Tagaroulias was out having pizza and pasta for lunch with his wife and son when the protesters went by. He said he had to delay his exit from the restaurant and was a little worried for his car parked on the road outside.

While the car was fine, Mr Tagaroulias said he was surprised at the level of participation in the march. "It was a bit of a shock," he said.

Asked what he thought of the strike, the 58-year-old said he thought it made people think about their impact on the environment, but he "would rather people think about it at home".

"I always point out to locals that they're hypocrites, because they're telling somebody else to do something and what we don't do is do the right thing ourselves," he said. "So there's a lot of things we can do here.

"I sometimes compare electricity bills with my peers in the same age group and same demographic, and I'm always astounded how much power they consume. That's one thing. The kinds of cars people drive; I think we can have an impact there, and how much we actually proactively recycle."

School Strike 4 Climate events were also held in Cessnock and Maitland.

Hunter MP Joel Fitzgibbon attended the Cessnock rally and told attendees he wanted "climate justice too".

"Australia is changing our ways, our take up on renewables is just amazing, but we need to progress those changes further," he said.

"But as a contributor of about only 1.3 per cent of the global emissions, our task is really an easy one

"The real challenge is to get emissions down in countries like China, which of course is responsible for about a third of global emissions. And we can't expect China to listen to us if we are not ourselves fulfilling our commitment."

The climate strikes held around Australia were considered the biggest nationwide protest turnout since 500,000 Australians took to the streets to protest against the Iraq war in 2003.

Organisers said "well over" 300,000 people gathered across the eight capital cities and more than 100 towns.

In a statement, School Strike 4 Climate said about 100,000 people rallied in Melbourne, 80,000 in Sydney, 30,000 in Brisbane, 20,000 in Hobart 15,000 in Canberra and 10,000 each in Adelaide and Perth.

An estimated 2500 Australian businesses also allowed their workers to attend and 33 Australian unions participated in events.

Police praised the conduct of strikers at the rallies in Newcastle and Sydney.

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