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In a global exclamation of defiance and solidarity, millions rallied at women's marches in the nation's capital and cities around the world Saturday to send President Donald Trump an emphatic message on his first full day in office that they won't let his agenda go unchallenged.

"Welcome to your first day, we will not go away!" marchers in Washington chanted.

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Organizers of the Women's March on Washington said the demonstrations were scheduled for the day after the presidential inauguration as a direct response to Trump, whose stances on abortion, immigration, climate change and health care have troubled participants. An estimated 500,000 people participated in the massive march on the nation's capital, D.C.'s deputy mayor for public safety and justice said, citing the event's organizers.

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Worldwide, including in London, Berlin and Tokyo, an estimated 3 million people participated in the march, according to organizers. Here are some of the demonstrations throughout the country and around the world:

New York City

Hundreds of thousands of people were estimated to have attended a rally and march in New York City, with a final stop along Fifth Avenue toward Trump Tower.

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Rosie Perez, Whoopi Goldberg, and Taylor Schilling of "Orange is the New Black" helped kick off the march.

Take a look at some of the signs from the #WomensMarch on NYC https://t.co/Fe3nMO7Z6n pic.twitter.com/1KRB0UqFBM — NBC New York (@NBCNewYork) January 21, 2017

Plenty of men seem to be heading to the women's march in NYC pic.twitter.com/yHR7ryeJ3D — Chris Jansing (@ChrisJansing) January 21, 2017

Chicago

Organizers initially estimated at least 75,000 people, but the march grew to roughly 250,000, as groups descended on a rally site at Columbus and Jackson, reported NBC Chicago.

Crowds have begun dispersing and roads are slowly being reopened. #WomensMarchChi has been peaceful. — Chicago Police (@Chicago_Police) January 21, 2017

Denver

Atlanta

Rep. John Lewis, D-Ga., a longtime civil rights leader, told the crowd at the Georgia State Capitol to continue to fight against injustice.

"Never, ever give up. Never lose hope," Lewis said. "We're fighting for our sisters and mothers and our daughters — we’re also fighting for our fathers and our sons and for people who can’t fight for themselves."

About 63,000 people attended the march, much higher than the 20,000 anticipated, according to the NAACP and Georgia State Patrol.

Philadelphia

Boston

Never seen a crowd like this in Boston. Not sure there is room to even march. #womensmarch pic.twitter.com/iv1HShAkue — Ryan D. Enos (@RyanDEnos) January 21, 2017

San Jose, California

Mayor Sam Liccardo said the crowd was estimated at about 25,000 people.

Los Angeles

Crowds of "well past" 100,000 people took part in demonstrations in downtown, the Los Angeles Police Department said. There were no arrests reported. "The women, men, and children exercised their first amendment rights in a joyous and peaceful manner," the LAPD said in a statement.

These LA marchers played drums and danced their way down the street picking up more people along the way #WomensMarch #womenmarchla @nbcla pic.twitter.com/drmluAl0x2 — Angie Crouch (@AngieNBCLA) January 22, 2017

Seattle

Organizers estimated the crowd in Seattle at 170,000 and at one point the march stretched for three miles, NBC affiliate KING 5 reported.

Quite possible that #WomensMarchSeattle will stretch from Seattle Center (destination) to Judkins Park (origin). That's 3 MILES of people! — Seattle Police Dept. (@SeattlePD) January 21, 2017

London

Proud to support women's rights with the whole fam in #womensmarchlondon pic.twitter.com/fzTtnIA4LP — Lin-Manuel Miranda (@Lin_Manuel) January 21, 2017

Paris

Several thousand are marching in #Paris as part of global #WomensMarch events pic.twitter.com/yQAyWiCrtL — catherine viette (@cathyruthi) January 21, 2017

Berlin

Antarctica

Alaska