The global climate strike is inspired by the 16-year-old Swedish activist Greta Thunberg.
Hundreds of thousands of students and workers left their schools, colleges and offices on Friday to take to the streets around the world and demand that world leaders take urgent measures to avoid an environmental catastrophe.
The global climate strike, inspired by Swedish activist Greta Thunberg, 16, began on the Pacific Islands and followed the rising sun in Australia, Japan, Southeast Asia and then in Europe, Africa and the Middle East.
It will culminate in New York when Thunberg, who has been nominated for a Nobel Peace Prize, will lead a demonstration at the headquarters of the United Nations, where the heads of government will meet for a climate summit next week.
"It's about my future, not just my future, but the future of all my generation and all the generations that will come after ours," said 16-year-old Tristan Vancleef, among some 15,000 protesters who marched through downtown Brussels .
The banners in the Brussels march included "Great kids save the hot planet", "I won't go to school until they cool it" and "If it melts it ruins."
Protesters call on governments to take immediate measures to limit the harmful effects of man-made climate change.
Social media posts showed dozens of demonstrations, from a few dozen elementary school children in Abuja, Nigeria, to tens of thousands of people in cities in Hamburg, in Germany; to Melbourne, Australia; Kabul, Afghanistan; Lahore, Islamabad and Karachi among 26 cities in Pakistan; and the main cities of India.
"Our future on his shoulders," said a banner spread on a street by students in Berlin.
"Our oceans are rising, so are we," was a popular slogan on posters, including one wearing a student wearing a school uniform in Melbourne and another wearing a girl with a face mask in Calcutta, in eastern India.