From the Pacific Islands, many of which risk being inundated by rising seas, to New Zealand, Australia and Thailand, people took to the streets to call on governments to take urgent steps to tackle the climate crisis and prevent an environmental catastrophe.
Greta Thunberg, the 16-year-old Swede who inspired the climate strike, tweeted her support.
"Incredible pictures," she wrote from New York where she will lead the protest. "This is the huge crowd building up in Sydney. Australia is setting the standard!"
Protests were expected to take place in 110 towns and cities across Australia, the world's largest exporter of coal and liquid natural gas, with crowds calling on the government to commit to a target of net-zero carbon emissions by 2030.
At least 2,000 companies gave people time off in order to attend the rally, the Sydney Morning Herald reported.
Protests are planned in some 150 countries on Friday and will culminate in New York when Thunberg, who has been nominated for a Nobel prize for her activism on climate change, leads the march in the city where the United
Nations has its headquarters.
The UN summit brings together world leaders to discuss climate change mitigation strategies, including the move from fossil fuels to renewable energy sources.
(Excerpts from Aljazeera)