Nature Conservation Council executive director Cate Faehrmann said early estimates were that up to 150,000 people had marched in protests around Australia.

She told reporters that protesters wanted the parties to show a stronger commitment to reducing greenhouse gas emissions, and said a near-term target of cutting emissions by 30 percent by 2020 was needed. The Labor opposition has set a 2050 emissions target.

Police estimated the crowd in Melbourne at between 20,000 and 30,000, while in Sydney organisers said more than 28,000 people attended. A Sydney police spokesman declined to give a crowd estimate.

"Both major parties have credibility problems on climate change because of their failure to commit to the sort of deep cuts to greenhouse emissions in the next decade that are necessary to help prevent dangerous climate change," Wilderness Society national campaign director Alex Marr told the Sydney rally.

Australia and the United States have refused to ratify the Kyoto Protocol, which sets binding targets for carbon pollution by developed countries.

Australian Prime Minister John Howard says any global agreement must include big developing nations such as China and India.