Thousands of protesters including school students have gathered in Sydney as the national strike in favour of action on climate change begins.
The Global Strike 4 Climate is taking place in 110 towns and cities across Australia on Friday, with organisers demanding government and business commit to a target of net zero carbon emissions by 2030.
They are also campaigning for a transition to 100 per cent renewable energy.
In Sydney, protesters are congregating at the Domain to listen to speeches before marching to Hyde Park later in the afternoon.
Daniel, 15, from Fort Street High School in Sydney said young people "are demanding more than they're being offered".
"Seeing how many young people are coming out, I think the current politicians we've got might not stay in power for so long anymore, with with a new voting base coming in," he told AAP.
Asked about those who have criticised students for protesting, he said: "They shouldn't be commenting on this when we're the ones being affected."
Bridget, 12, from Chevalier College in the NSW Southern Highlands, had a message for the country's politicians: "Don't be a fossil fool".
"I'm concerned about this because I kind of want a future," she said.
"They didn't do anything when they were kids so they left it all up to us to fix."
One of the protesters included a man dressed as a yeti, holding a sign saying: "Wake up humans you're endangered too".
A woman dressed in a gold cape holding a sign which read: "Canary in a coal mine".
Global Strike 4 Climate organisers expect a 50 per cent increase in attendance from the most recent climate strike in March, which drew 150,000 protesters.
Universities have confirmed they will not penalise students for attending the rallies, while the Uniting Church synod for NSW and the ACT have backed their students to attend the demonstrations.
But Catholic and Anglican church-run schools say their students should remain in class, as do NSW public schools.
Acting Prime Minister Michael McCormack said students should be in school.
"I think these sorts of rallies should be held on a weekend where it doesn't actually disrupt business, it doesn't disrupt schools, it doesn't disrupt universities," Mr McCormack told reporters in Melbourne.
"I think it is just a disruption."
The strike is the latest in a worldwide movement started in August 2018 when 16-year-old Swedish climate activist Greta Thunberg began protesting outside Sweden's parliament on school days.
She'll participate in the UN's youth climate forum on Saturday and address world leaders at the UN secretary-general's climate summit on September 23.
Ms Thunberg is currently in the US after taking a yacht across the Atlantic to prevent carbon emissions, and urged US lawmakers to "listen to the scientists".
The next global strike is scheduled for September 27.
© AAP 2019