From London to New York City and from Perth to Paris, climate activists are taking part in a global general strike on Friday in what is expected to be the biggest day of climate demonstrations in the planet's history.

Some of the first protests were held in Australia and organizers have said "well over" 300,000 people gathered at more than 100 cities and towns across the country. Melbourne hosted the biggest march, according to organizers, with 100,000 people turning out, while 80,000 rallied in Sydney and 30,000 in Brisbane.

The Global Climate Strike is the third in a worldwide series of climate rallies organized by school students, and led by 16-year-old Greta Thunberg. Protestors hope to put pressure on politicians and policymakers to act on climate issues.

Thousands crowd a street during a climate protest in Brussels.
Thousands crowd a street during a climate protest in Brussels.
Francisco Seco/AP
A student leads others to an exit past the translucent red walls of Seattle City Hall, while student climate activists protest outside.
A student leads others to an exit past the translucent red walls of Seattle City Hall, while student climate activists protest outside.
Elaine Thompson/AP
Amazon employees march from the company's headquarters past the campus "spheres" in Seattle.
Amazon employees march from the company's headquarters past the campus "spheres" in Seattle.
Elaine Thompson/AP
A demonstrator representing the Amazon rainforest performs during a protest in Brasilia, Brazil.
A demonstrator representing the Amazon rainforest performs during a protest in Brasilia, Brazil.
Eraldo Peres/AP
Thousands march through the streets in downtown Los Angeles.
Thousands march through the streets in downtown Los Angeles.
Frederic J. Brown/AFP/Getty Images
Greta Thunberg, center, walks with protesters during the Global Climate Strike march in New York.
Greta Thunberg, center, walks with protesters during the Global Climate Strike march in New York.
Timothy A. Clary/AFP/Getty Images
Protesters march through Brussels.
Protesters march through Brussels.
Jack Taylor/Getty Images
People rally in Hamburg, Germany.
People rally in Hamburg, Germany.
Axel Heimken/dpa via AP
Students chant as they gather at the state Capitol in Austin, Texas.
Students chant as they gather at the state Capitol in Austin, Texas.
Eric Gay/AP
People protest in La Paz, Bolivia.
People protest in La Paz, Bolivia.
Juan Karita/AP
Students take part in a rally in Kiev, Ukraine.
Students take part in a rally in Kiev, Ukraine.
Pavlo Gonchar/SOPA Images/LightRocket via Getty Images
Students gather on the steps of the Statehouse in Indianapolis, Indiana.
Students gather on the steps of the Statehouse in Indianapolis, Indiana.
Darron Cummings/AP
Around a thousand protesters, some wearing outfits made from plastic bottles and bottle-tops to raise the issue of plastic pollution, march in the streets of Nairobi, Kenya.
Around a thousand protesters, some wearing outfits made from plastic bottles and bottle-tops to raise the issue of plastic pollution, march in the streets of Nairobi, Kenya.
Ben Curtis/AP
People march in Sydney, Australia.
People march in Sydney, Australia.
Cordelia Hsu/Reuters
A participant dressed up as an injured earth marches in Stuttgart, Germany.
A participant dressed up as an injured earth marches in Stuttgart, Germany.
Sebastian Gollnow/picture alliance via Getty Images
People hold placards as they march in Lahore, Pakistan.
People hold placards as they march in Lahore, Pakistan.
ARIF ALI/AFP/Getty Images
Demonstrators fill the Jungfernstieg, a promenade in Hamburg, Germany.
Demonstrators fill the Jungfernstieg, a promenade in Hamburg, Germany.
citynewstv/picture-alliance/dpa/AP
Protesters lie on the ground near the Ministry of Natural Resources and Environment in Bangkok.
Protesters lie on the ground near the Ministry of Natural Resources and Environment in Bangkok.
Soe Zeya Tun/Reuters
People in Krakow, Poland, march.
People in Krakow, Poland, march.
Omar Marques/SOPA Images/LightRocket via Getty Images
Protesters fill a street in Edinburgh, Scotland.
Protesters fill a street in Edinburgh, Scotland.
Jeff J Mitchell/Getty Images
Activists block a road in Frankfurt, Germany, during rush hour.
Activists block a road in Frankfurt, Germany, during rush hour.
Michael Probst/AP
Protesters march in Johannesburg, South Africa.
Protesters march in Johannesburg, South Africa.
Michele Spatari/AFP/Getty Images
Climate change protesters cross the Victoria Bridge in Brisbane, Australia.
Climate change protesters cross the Victoria Bridge in Brisbane, Australia.
Darren England/AAP Image/Reuters
A protester wears a gas mask during a march in Gauhati, India.
A protester wears a gas mask during a march in Gauhati, India.
Anupam Nath/AP
Protesters participate in the UK Student Climate Network's demonstration in London.
Protesters participate in the UK Student Climate Network's demonstration in London.
Gareth Fuller/PA Wire/AP
Climate protesters demonstrate in Athens, Greece.
Climate protesters demonstrate in Athens, Greece.
Thanassis Stavrakis/AP
Activists take part in a demonstration in Lublin, Poland.
Activists take part in a demonstration in Lublin, Poland.
Jakub Orzechowski/Agencja Gazeta via Reuters