Check back for more additions and updates as the #ClimateStrike continues on Friday...

Kicking off what organizers say will be the largest mass climate demonstration in history, millions of young people and their adult allies flooded the streets around the world Friday to take part in the Global Climate Strike and pressure world leaders to confront the ecological crisis with bold and urgent action.

According to 350.org, over 4 million people took part in the collective demonstrations worldwide.

"Today we saw a movement, made up of people from all ages and backgrounds coming together and calling for the end of coal, oil, and gas. No matter what differences we have, we are together now because we are fighting for our future," said May Boeve, executive director of 350.org, in a statement. "September 20th was a demonstration of intent, of four million people who took time off from work or school to say that they are ready. Ready to move on and make the changes we need for a future free from fossil fuels and based in climate equity and justice. And it was only the beginning."

An estimated 400,000 people gathered in Australia alone as hundreds of thousands of others rallied across India, Germany, Austria, Indonesia, Kenya, Pakistan, the U.K., and other nations.

"We have no choice but to act when the alternative is to sit and watch our world burn. We have no choice but to act when the alternative is extinction."

—Vic Barrett

"We're here to reclaim our right to live, our right to breathe, our right to exist," said youth climate activist Aman Sharma, who gathered with thousands in Dehli.

Demonstrations are expected to take place in over 130 nations on Friday, with more than 800 strikes planned in the United States. "I think it's pretty clear this will be the biggest day of climate action in planetary history," said 350.org founder Bill McKibben on Friday as images and videos began to pour in on social media.

The strikes, led by youth climate activists, have drawn enthusiastic support from diverse segments of society, including teachers, scientists, tech workers, labor unions, and lawmakers.

Vic Barrett, a 20-year-old plaintiff in the Juliana v. United States climate lawsuit against the American government, wrote in an op-ed for The Guardian Friday that he is taking part in the Global Climate Strike because "this decade is our last chance to stop the destruction of our people and our planet."

"We have no choice but to act when the alternative is to sit and watch our world burn," wrote Barrett. "We have no choice but to act when the alternative is extinction."

On social media, #ClimateStrike photos and videos were flooding platforms like Twitter with an on-the-ground look from cities and countries from around the world.

Freiburg, Germany:

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

Sydney, Australia:

Tokyo, Japan:

In Tokyo, we also step up to support young climate strikers and demand an end to the age of fossil fuels #ClimateStrike #FridaysForFuture #ClimateEmergency pic.twitter.com/a2KLuQ6mEu — Chema Sarri (@chemasarri) September 20, 2019

Nariño, Colombia:

10,000 people joined the #ClimateStrike in Nariño, Colombia.



It was beautiful.



Photo credit: Xiomara Acevedo pic.twitter.com/w1evdLJ15U — 350 dot org (@350) September 20, 2019

Quezon City, Philippines:

Paris, France:

Lahore, Pakistan:

Dublin, Ireland:

New Delhi, India:

Hundreds of young activists participated in the climate protest in the Indian capital of New Delhi.



#FridaysForFuture #ClimateStrike #climateaction



Via @TheMayankChawla



pic.twitter.com/GTzLi1TGeL — Greenpeace India (@greenpeaceindia) September 20, 2019

Woerdern, Austria:

Funafuti, Tuvalu:

São Paulo, Brazil:



@GretaThunberg Members of Brazil's Landless Rural Workers Movement outside HQ of German multinational Bayer in São Paulo as part of the Global #ClimateStrike. They protested x climate protection and against the anti-environmental policies of @jairbolsonaro pic.twitter.com/1KssIDcfXC — (@ottawaluis) September 20, 2019

Cape Town, South Africa:

South Africa sure knows how to Protest in Style #ClimateStrike pic.twitter.com/9cvavjKCMt — Labour's Black PLP (@LaboursBlackPLP) September 20, 2019

New York City:

Thousands of young people are gathering in Foley Square to march in the streets of New York City. #ClimateStrike #GlobalClimateStrike pic.twitter.com/2D1NtXlBFe — Zac (@ThingsZacThinks) September 20, 2019 New York City is looking huge! Lower Manhattan is absolutely packed with people. It will take ages for everyone to get to Battery Park.#ClimateStrike #FridaysForFuture pic.twitter.com/InoX8kQmCa — Greta Thunberg (@GretaThunberg) September 20, 2019

San Francisco, California:

Thousands of young people in San Francisco for the youth-led #ClimateStrike!



There is hope for our future and our planet! #ClimateJustice #ClimateJusticeNow pic.twitter.com/zHrjUXr4bO — Alyssa Kang (@1alyssakang) September 20, 2019

Philadelphia, Pennsylvania:

London, England:

Everybody London #ClimateStrike is massive. I think I’m gonna cry pic.twitter.com/44OR451v6f — Hannah Martin (@Hannah_RM) September 20, 2019

Stratford-Upon-Avon, England:

England and the UK lead with significant turnout! What are we doing? #Toronto? @JohnTory where is your statement? Mayors of London, Paris New York, Los Angeles, Copenhagen issued a fantastic statement. #ClimateStrike https://t.co/GilhHV1v1Y — Neva RvW (@n_weva) September 20, 2019

Katmandou, Nepal:

Ceará State, Brazil:

"Oil, gas and coal, must stay in the ground" people in Fortaleza, Ceará State, Brazil are asking for climate justice! José Rafael in Luiza Távora square. #mobilizaçãopeloclima #ClimateStrike pic.twitter.com/p3Q05tTFSZ — 350 dot org (@350) September 20, 2019

Antarctica:

Climate change is not a possibility for the distant future, it is the REALITY OF TODAY!!! It’s time to rise before it’s too late. We support you, climate strikers. With love and hope from Antarctica.#ClimateStrike #FridaysForFuture pic.twitter.com/Z4AoIuPXWw — Dr. Kim Bernard (@psycho_kriller) September 20, 2019

And in photos from around the world, the size of the demonstrations and the passion of those striking was palpable.

In Germany:

In Indonesia:

In Kenya:

In India:

In Scotland:

In Turkey:

In England:

Check back for more additions and updates as the #ClimateStrike continues on Friday...