Thousands of young Australians walking out of their classrooms to demand action on climate change have joined rallies in cities and towns around the country.
Thousands of students and adults are also joining climate rallies in cities and towns across the world, international media report.
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.
Demonstrations were officially registered in all eight capital cities and 104 other towns across Australia.
More than 2,500 Australian businesses have pledged to participate in the action, 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".
Tens of thousands turned out at The Domain in Sydney for the rally there.
There were reports of packed buses with students with signs coming into the city, with huge numbers marching through the CBD.
In Hobart, thousands of protesters gathered at the lawns outside Parliament House.
Johanna Ellis, 21, said her workplace had closed for the day, "but we're still getting paid to rally".
The protesters focused on how climate change is affecting Indigenous people in remote communities.