Climate activists gathered on the steps of Sydney's iconic Opera House on Saturday and along the city's beaches to kick off an international day of protest about global warming.
Along the famous sands of Bondi Beach and across the span of the Harbour Bridge protesters gathered with placards bearing the logo 350 to call for a cut in carbon emissions to 350 parts per million (ppm), organisers said.
Thousands of people gathered on the steps of the Opera House for an outdoor concert and formed a giant 350 with their bodies, one of more than 200 events to be staged across the continent, said spokeswoman Blair Palese.
Church bells at the city's largest cathedral sounded 350 times, while groups ranging from scuba divers to Frisbee players gathered to stage events Australia-wide.
Similar stunts were planned at some 4,000 locations in more than 170 countries across the globe, including the Eiffel Tower, Times Square and the Himalayas, said Palese.
The protest marks 50 days until world leaders meet in Copenhagen to thrash out a new climate change treaty.
"Our global emissions are now perilously high, at 387 ppm," Palese said.
"The majority of expert scientists now say this has to come down to 350 ppm to avoid dangerous climate change. 350.org is calling for our political leaders make this their target."
Australia has committed to cutting greenhouse gas emissions by up to 25 per cent by 2020 compared to 2000 levels if an "ambitious" target is agreed in Copenhagen.