(Reuters) - Millions of young people flooded the streets of cities around the world on Friday to demand political leaders take urgent steps to stop climate change, uniting in a worldwide protest inspired by 16-year-old Swedish activist Greta Thunberg.

Alarmed by images of the Greenland ice sheets melting and the Amazon rain forests burning, students and workers abandoned schools, shops and offices in nearly every corner of the globe, aiming to stop what they see as a looming environmental catastrophe.

The protests started in the Pacific islands, where rising sea levels threaten a way of life, and followed the sun across Australia, Japan, Southeast Asia and on to Europe, Africa, the Middle East and the Americas. The coordinated student “strike” culminated in New York’s Wall Street, where some investors have embraced the fossil fuel industry.

Massive crowds overwhelmed the streets of lower Manhattan, chanting “Save our planet!” while anticipating an address by Thunberg, an international figure who sailed across the Atlantic in an emissions-free yacht ahead of next week’s climate summit at the United Nations.

“Right now we are the ones who are making a difference. If no one else will take action, then we will,” Thunberg told tens of thousands of people gathered at a park with a view of the Statue of Liberty.

Once she took the stage, the crowd chanted her name, then went silent to hang on her every word. As she paused between sentences, people erupted into applause.

“If you belong to that small group of people who feel threatened by us, then we have some very bad news for you. Because this is only the beginning. Change is coming whether they like it or not,” she concluded.

Demonstrators in Paris raised a painting of Thunberg as the Virgin Mary, a halo around her head reading, “Our house is on fire.”

“She’s like the icon of our generation,” New York protester Fiamma Cochrane, 17, said, highlighting the leadership role of young people in the international movement to reduce consumption of fossil fuels.

Four million people participated worldwide including 300,000 in New York, organizers with the anti-fossil fuels group 350.org said. Reuters could not verify the crowd sizes.

Concern has escalated since U.S. President Donald Trump abandoned the international Paris Accord on climate change and took a series of steps to dismantle environmental protections, including moving on Thursday to block stricter vehicle emissions standards in California.

Trump and Brazilian President Jair Bolsonaro are among the world’s only national leaders who publicly question the science of climate change, and they are not taking part in next week’s U.N. climate summit.

Thousands gathered across Brazil to take aim at Bolsonaro, who they say is allowing the destruction of the Amazon rainforest to clear space for soy beans and cattle ranching. In August, fires there surged to their greatest level since 2010.

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“The policy of the Bolsonaro government is the policy of environmental destruction and deepening the climate crisis ... this is why we’re on strike,” said Marcela Pimentel Miranda, an organizer for Youth for Climate’s affiliate in Brasilia.

One protester in Sao Paulo held up a picture of Bolsonaro and Trump beneath the hand-written “Abolish fossil fools!”

Demonstrators in Thailand stormed the environment ministry and feigned death, while activists in Berlin and Munich stood on melting blocks of ice with nooses around their necks to symbolize the earth’s fate when the polar ice caps melt.

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Protesters in Warsaw staged a performance of people drowning in a sea of plastic waste.

“The planet is getting hotter than my imaginary boyfriend,” read a poster held by a teenager in Thailand.

“Make love, not CO2” signs were spotted in Berlin and Vienna.

While Europeans filled the streets, students in the Solomon Islands gathered at the rising ocean water’s edge wearing traditional grass skirts. The issue is vital to low-lying Pacific islands, which have repeatedly asked wealthier nations to do more to prevent rising sea levels.

Global warming caused by heat-trapping greenhouse gases from burning fossil fuels has already led to droughts and heat waves, melting glaciers, rising sea levels and floods, according to scientists.

“There is no Planet B,” read a sign hoisted by a young woman in London.

In Kenya, around 500 activists marched to demand that the government cancel plans for a coal plant and investigate corruption in hydropower dams.

“In Samburu there is a lot of heat, the grass has dried up, there is little water,” said Francis Lentel, a young herdsman in traditional beads, holding a picture of the Earth weeping.

The protest movement is putting increasing pressure on governments and companies to respond.

German Chancellor Angela Merkel unveiled a new climate protection package thrashed out by parties in her coalition during all-night talks.

Private industry has also responded. Amazon.com Inc Chief Executive Officer Jeff Bezos on Thursday pledged to make the largest U.S. e-commerce company net carbon neutral by 2040.

Hundreds of workers from Google, Amazon and other technology companies on Friday criticized their industry for being slow to tackle climate change and joined marches in San Francisco and Seattle calling for action.