Organisers estimate 300,000 Australians have gathered at climate change rallies around the country in one of the largest protest events in the nation's history.

Key points: The protests are part of a global strike movement led by a 16-year-old Swedish activist

The protests are part of a global strike movement led by a 16-year-old Swedish activist More than 2,500 Australian businesses said they were participating in the strike

More than 2,500 Australian businesses said they were participating in the strike More conservative estimates had the number closer to 180,000 demonstrators

The global day of action, led by Swedish teenage climate activist Greta Thunberg, is happening three days before the United Nations Climate Change Summit in New York.

Organisers say they expect millions of people to turn out worldwide in 150 countries.

In Australia, demonstrations took place in all eight capital cities as well as 104 other centres.

The Australian protesters called for the Federal Government to commit to:

No new coal, oil or gas projects

No new coal, oil or gas projects 100 per cent renewable energy generation and exports by 2030

100 per cent renewable energy generation and exports by 2030 Funding for "a just transition and job creation for all fossil fuel industry workers and communities"

Thousands gathered in Sydney's Domain. ( ABC News: Brendan Esposito )

The movement has rallied behind 16-year-old Thunberg, who first started protesting alone outside Sweden's Parliament last year.

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As the Australian protests began she tweeted in support.

"Incredible pictures as Australia's gathering for the #climatestrike This is the huge crowd building up in Sydney. Australia is setting the standard! Its bedtime in New York...so please share as many pictures as you can as the strikes move across Asia to Europe and Africa!"

The movement has been controversial in Australia, with some teachers being accused of bias and bringing politics into the classroom, and the Federal Government linking the demonstrations to flagging test results.

More than 2,500 Australian businesses took part, either closing their doors or allowing their employees to walk off the job.

The businesses signed on to Not Business As Usual, an alliance which said it was a "group of Australian and global businesses pledging to support worker participation in the climate strike".

The exact number of demonstrators nationally was unclear, but more conservative estimates put the number closer to 180,000.

The centres of Melbourne, Sydney and Brisbane were brought to a standstill as the protests snaked their way through CBD streets.

Children climbed a rig in Sydney to make their voice heard at the global climate strike. ( ABC News: Brendan Esposito )

Organisers initially said 150,000 people turned out to march in Melbourne, before the number was revised down to 100,000. Victoria Police declined to provide an estimate of crowd numbers.

Organisers said 150,000 attended the rally in Melbourne. ( ABC News )

The Pacific Climate Warriors performed in Melbourne, calling for action to protect Pacific nations from rising sea levels. ( ABC News: Andie Noonan )

Tens of thousands turned out at The Domain in Sydney. Organisers placed the number at 80,000 people.

In Brisbane, organisers estimated more than 35,000 people were in attendance. Queensland Police said the figure was closer to 12,000.

Year 8 student Audrey Mason Hyde, 14, attended the climate strike in Adelaide. ( ABC News: Shuba Krishnan )

The rally was approved by Brisbane City Council but criticised by both sides of politics, with Queensland Education Minister Grace Grace arguing student protests should take place outside school hours.

Thousands of people marched across the Victoria Bridge in Brisbane. ( Supplied: Shannon Iwanow )

Marching with his classmates, 10-year-old Parker Renshaw said he and his fellow students were fearful for their future.

"I would love to be in school at the moment but it's not much choice to be here, the Government is forcing us to come.

"My education is important but the world is even more important and we need to help it."

Passions were high at the climate strike in Melbourne. ( ABC News: Andie Noonan )

In Hobart, thousands of protesters gathered at the lawns outside Parliament House.

"Activism is education and this is our classroom," teen activist Toby Thorpe told a cheering crowd.

"But we're not the students here, we are the teachers, and we will not stop until we're heard."

Johanna Ellis, 21, said her workplace had closed for the day, "but we're still getting paid to rally".

Organisers put the figure at 22,000 in Hobart, while police said they could not confirm crowd numbers.

On social media, former Greens leader Bob Brown said the turnout was bigger than the iconic Franklin River dam protests in the 1980s.

In Perth, where organisers put the figure at 10,000 demonstrators, small children marched with their parents and high school students from Forrest Place to Elizabeth Quay.

Johanna Ellis left work to attend Hobart's rally. ( ABC News: Charley Rico )

In Canberra, thousands marched through the city and gathered in Glebe Park, demanding action from Australia's leaders.

"It's important that our Government hears out our youth and what we have to say," one protester said.

Students marched through Canberra to make their voices heard. ( ABC News: Greg Nelson )

More than 8,000 students in Adelaide marched through Victoria Square to South Australia's Parliament House.

"I'm here because we need to stop it now, we're running out of time to sort this mess out," Year 9 student Archie Salmond said.

"It's all going by too fast. If we don't fix it, no one will, and it just needs to be stopped."

Students in an RMIT University engineering course attending Melbourne's rally were offered assignment marks for marching, the university confirmed.

"Students in this course are currently completing a design project, and a component of this project relates to environmental impact and ethics," a university spokesperson said.

"While the teacher has determined that the conversation at today's global climate strike is educational and relevant to the learning for this project, RMIT will of course be looking at the decision to ensure that assessment integrity is maintained."

Large crowds of all ages gathered in Melbourne's Treasury Gardens. ( ABC News: Andie Noonan )

'We're the ones that are going to be impacted by this'

Piper Lily O'Connell, 17, was one of the school students who organised the Cairns rally. ( ABC News: Jesse Thompson )

Cairns organiser Piper Lily O'Connell said many Queensland protesters were focused on stopping the Adani Carmichael coal mine.

"We're in the thick of a climate crisis right now, in Australia, but especially in Cairns we feel that pretty strongly. The Great Barrier Reef is on our doorstep and dying.

"These are pretty scary things and as a teenager … we're the ones that are going to be impacted by this."

Climate activists in Cairns used colours, signs and costumes to make their point. ( ABC News: Jesse Thompson )

Alpine communities also joined the protest with locals at Mount Hotham in Victoria expressing deep concern about global warming. ( Supplied: Karl Gray )

In Alice Springs more than 500 people attended the climate strike in the Todd Mall, with school students making up a large portion of the crowd.

The protesters focused on how climate change is affecting Indigenous people in remote communities.

In Alice Springs, demonstrators held a 'die-in' at the Todd Mall. ( ABC News: Katrina Beavan )

Hundreds of people rallied in Townsville during the morning, many missing work and school.

"It's our future and we care so much about our future and that is why we are here," 13-year-old Ella Rizos said.

In Townsville, students used Dr Seuss to get their message across. ( ABC News: Hannah Palmer )

Students in the remote Northern Territory town of Tennant Creek did not go on strike, but staged a protest in their schoolyard which faces a major highway.

School attendance is a huge issue across the NT, and the school community decided it was inappropriate to encourage students to skip school for the day.

Tennant Creek Primary School has an attendance rate of 67 per cent, which is higher than many other remote NT schools. ( ABC News: Steven Schubert )

Sian (right) from Devonport in Tasmania attended the rally on crutches with her friend Ruby. ( ABC News: Henry Zwartz )

Australia's emissions continue to climb

The protests were spurred on by the Intergovernmental Panel on Climate Change (IPCC) report released last year that detailed a catastrophic future of extreme weather events if greenhouse gas emissions were not reined in.

The United Nations released a report in February showing that the 20 warmest years on record had all been in the past 22 years.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 33 seconds 1 m 33 s Student activists in Melbourne explained why they skipped school to attend the demonstration.

Australia is a signatory to the 2015 Paris climate agreement, the global deal to combat climate change, and pledged to reduce the country's emissions by 26 to 28 per cent from 2005 levels by 2030.

Figures released in August showed Australia's carbon emissions were continuing to climb.

Many people brought signs to the climate rally in Perth. ( ABC News: Rhiannon Shine )

Data released in June showed Australia's pollution was at an all-time high across most sectors.

Environment Minister Sussan Ley said if the purpose of the protest was to draw Government attention to climate change "I can assure everyone that our attention is already there".

"We are taking real and coordinated global action on climate change, while ensuring our economy remains strong," she said in a statement.



In a statement, Education Minister Dan Tehan drew a link between the global strike movement and flagging test results around the country.

"The true test of the protesters' commitment would be how many turned up for a protest held on a Saturday afternoon," he said.

Tens of thousands of protesters marched through Brisbane's CBD. ( ABC News: Kerrin Binnie )

A boat at Hobart's waterfront took part in the demonstrations. ( ABC News: Charley Rico )

Protesters in Townsville joined more than 100 other Australian towns urging action on climate change. ( ABC News: Hannah Palmer )