Activists across over 150 countries are participating in an international strike Friday to protest climate change. High profile protesters – such as Greta Thunberg, who helped inspire the student-led protests by starting school walkouts in her hometown – are leading dozens of mass rallies across the United States.

The global strike, set just days before September 23’s U.N. Climate Action Summit in New York, is expected to draw millions of activists, who believe human activity is contributing to climate change and that drastic measures – such as limiting meat consumption, reforming the transportation sector, and banning plastic straws – need to be taken in order to combat the looming threat.

Videos are surfacing from protests across the globe, showing sizable crowds in places like Ireland, Germany, Australia, Uganda, and more:

Look at the massive, gorgeous crowd in Kampala Uganda for #ClimateStrike. The planet's running a fever and the antibodies are kicking in! https://t.co/9iqOnXv5at — Bill McKibben (@billmckibben) September 20, 2019

The estimate is at least 70,000 on #ClimateStrike in beautiful Cologne, Germany. The numbers around the world are astonishing https://t.co/BfGN3bCaU9 — Bill McKibben (@billmckibben) September 20, 2019

Like the sea we rise!

Liebes Klimakabinett, ihr habt euch mit den falschen angelegt…#AlleFuersKlima #FridaysForFuture pic.twitter.com/RW5jn9RnWf — Fridays for Future Freiburg (@F4F_Freiburg) September 20, 2019

The Edinburgh #climatestrike is easily one of the biggest marches ever seen at the Scottish Parliament. The message is clear: we need radical action to protect our future, and we need to take it now. 🌍 pic.twitter.com/N8vZSYYJRS — Scottish Greens (@scotgp) September 20, 2019

From Melbourne to Nairobi, London to New Delhi. People fill the streets around the world in the global #climatestrike. pic.twitter.com/6A5S4wtC9f — Channel 4 News (@Channel4News) September 20, 2019

The #ClimateStrike crowd numbers are phenomenal.

Melbourne 100,000+

Sydney 80,000+

Brisbane 30,000

Hobart 20,000

Canberra 15,000

Perth & Adelaide at least 10,000 each

Thousands more across regional Australia & Pacific https://t.co/rViiPMOgWR @strikeclimate #schoolstrike4climate pic.twitter.com/VAOKRHq7Zu — Guardian Australia (@GuardianAus) September 20, 2019

Labour Party leader Jeremy Corbyn participated in the climate strikes in London and condemned President Trump for pulling out of the Paris Climate Agreement.

“No more of this handholding with Donald Trump,” he told the crowd. “We want every country on board on this”:

"No more of this handholding with Donald Trump". Jeremy Corbyn criticises the US president for pulling America out of the Paris climate agreement at the #ClimateStrike today. Good — our world needs a leader with the balls to stand up to Trump ✊pic.twitter.com/HfseNvmVoT — Corbyn for PM (@CorbynASAP) September 20, 2019

This #ClimateStrike is inspiring – full of young people who are demanding change to protect our planet and their future. Labour will honour that demand by kickstarting a Green Industrial Revolution. pic.twitter.com/avaExj8wKe — Jeremy Corbyn (@jeremycorbyn) September 20, 2019

There are also climate strikes taking place in major cities across the U.S., including Boston, San Francisco, Seattle, D.C., and New York City. Famed teen activist Greta Thunberg – who sailed to the U.S. in order to avoid making a massive carbon footprint – will participate in the climate strike in New York City, where over one million students have been given permission to skip class in order to protest climate change:

.@NYCschools will excuse absences of students participating in the #ClimateStrike on Friday 9/20. Students will need parental consent. Younger students can only leave school with a parent. https://t.co/hcBO1Cnb3m — NYC Public Schools (@NYCSchools) September 12, 2019

Many Democrat presidential candidates are praising the effort as protests continue to kick-off across the nation.

“There is nothing more powerful than our nation’s youth marching together, demanding action be taken to protect our planet — and their future,” Sen. Kamala Harris (D-CA) wrote. “It’s time our leaders listened. #ClimateStrike”:

There is nothing more powerful than our nation’s youth marching together, demanding action be taken to protect our planet — and their future. It’s time our leaders listened. #ClimateStrike — Kamala Harris (@KamalaHarris) September 20, 2019

“Climate change is an existential threat—and we are already facing the effects. The youth-led #ClimateStrike and the solidarity strikes from groups like @AMZNforClimate show that our country is ready to fight for the big, structural change we’ll need to tackle the climate crisis,” Sen. Elizabeth Warren (D-MA) tweeted:

Climate change is an existential threat—and we are already facing the effects. The youth-led #ClimateStrike and the solidarity strikes from groups like @AMZNforClimate show that our country is ready to fight for the big, structural change we'll need to tackle the climate crisis. — Elizabeth Warren (@ewarren) September 20, 2019

“Young people have already demonstrated they can take on powerful fossil fuel companies and force politicians to answer their call to action,” Sen. Bernie Sanders (I-VT) wrote.

“To the millions of young people and allies worldwide who are striking today to demand climate justice: I stand with you. #ClimateStrike,” he added:

Young people have already demonstrated they can take on powerful fossil fuel companies and force politicians to answer their call to action. To the millions of young people and allies worldwide who are striking today to demand climate justice: I stand with you. #ClimateStrike pic.twitter.com/MzNXI4XIjK — Bernie Sanders (@SenSanders) September 20, 2019

“Our planet is in crisis—but we aren’t powerless to combat it,” Sen. Cory Booker (D-NJ) declared. “Inspired by the young people leading on today’s #ClimateStrike and committed to standing alongside them in the battle against climate change”:

Our planet is in crisis—but we aren't powerless to combat it. Inspired by the young people leading on today's #ClimateStrike and committed to standing alongside them in the battle against climate change. https://t.co/xk15EskiLx pic.twitter.com/dX21RHonoL — Cory Booker (@CoryBooker) September 20, 2019

The global strike follows Thunberg’s appearance before the House Committee on Foreign Affairs and Select Committee on the Climate Crisis. She submitted the United Nation’s IPCC Special Report on Global Warming as her written testimony, writing, “I am submitting this report as my testimony because I don’t want you to listen to me …I want you to listen to the scientists. And I want you to unite behind the science.”