Protest organisers, Stop Adani, estimated that 15,000 people had joined the marches across the country, while the Australian Youth Climate Coalition said that 5,000 people had marched in Melbourne alone.
The rallies follow last week's demonstrations urging action on climate change, which saw 15,000 school students walk out of class.
Australia has pledged to reduce total emissions to 26-28 percent below 2005 levels by 2030, but a recent UN report said there has been no improvement in the country's climate policy since 2017.
The document said the latest projections published by the government indicated that emissions would remain high rather than being reduced in line with the 2030 targets.
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