The rally drew almost double the numbers of December's "Sydney is Choking" rally.
Protesters turned out in droves to march across the landmark in support of immediate climate action.
Hundreds gathered to decry Scott Morrison and his government for their inaction on the ongoing bushfires.
20,000 rally in anger at government inaction on climate change, as Sydney sees unprecedented hazardous air quality.
A vignette of scientific takes on the largest student strike in recent memory
Nationwide demonstrations stopped cities to rally against the controversial coal mine
Strikes, rallies and marches take place as thousands protest climate inaction