WASHINGTON — Hundreds of thousands of demonstrators — predominantly women, but also men and children of all ages and races — on Saturday flooded the Capitol Hill area, where President Donald Trump had been inaugurated a day earlier, to stand up for reproductive, LGBT, immigrant and other rights they say his presidency threatens.

“We won’t go away. Welcome to your first day,” those with the Women’s March on Washington chanted, many wearing distinctive pink knit caps.

“We are the popular vote,” the participants said at other points, a reference to the nearly 3 million-vote margin Democrat Hillary Clinton had over Trump, a Republican, in the election.

Participants in the Women’s March on Washington numbered close to 500,000, according to the district’s deputy mayor in an unofficial estimate. That number would be more than double the number who said they would attend on the march’s official Facebook page.

The Washington Metropolitan Area Transit Authority tweeted that ridership on buses and trains as of 4 p.m had exceeded more than 597,000 trips. As a comparison, the transit agency said that as of 11 a.m. it had recorded 275,000 trips, compared to 193,000 trips in the same time frame on Inauguration Day.

“It’s a beautiful sight,” said Elizabeth Zimmermann, 58, of Lynbrook, of the crowd. She attended with her husband and two friends, her son and his girlfriend.

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“As women, we are teachers, protectors and nurturers. . . . We have to give a voice. We can’t go backward,” Zimmermann said, adding that her participation isn’t anti-Trump. “I’m tired of the us versus them; tired of the divide.”

Speakers, including feminist icon Gloria Steinem, actors America Ferrera and Scarlett Johansson and Sen. Kirsten Gillibrand (D-N.Y.), fired up demonstrators at a morning rally near the U.S. Capitol before marchers stepped off and streamed toward the White House. The march lasted until evening.

Steinem told the crowd: “The Constitution doesn’t start with ‘I, the president.’ It starts with ‘We, the people.’ ”

Gillibrand said the Women’s March marked a historic moment in the women’s rights movement. “This is the moment you will remember when women stood strong, and stood firm,” Gillibrand said.

Some of the marchers wore buttons or shirts with slogans favoring Hillary Clinton. Others had Bernie Sanders memorabilia. Many of the signs criticized Trump and his statements about women and expressing unity against his policies.

Ally Davis, 27, of Port Washington, held a pink sign that read: “Women’s rights are human rights.”

“He’s our president,” the graduate student acknowledged of Trump while adding, “but we need to make a statement to the administration that words of hate toward women, immigrants, refugees, LGBT communities aren’t something we’ll stand for.”

Holly Lavelli, 23, of Merrick, and her cousin, Ariana Lavelli, 22, of Yonkers, were invigorated by the huge crowds.

“As women, we all need to stick together and empower each other,” said Holly Lavelli, a Stony Brook University student.

The march seeks to call attention to reproductive rights, climate change and discrimination against minority communities. Organizers said they wanted to unite against the divisive environment they said Trump and Vice President Mike Pence have ushered in.

Julie Casey, a U.S Navy veteran, said she took “planes, trains and automobiles” to make it from her home in Bloomington, Illinois. “It’s suppose to be a positive occasion, to be surrounded by such empowering messages, but I can’t help but feel sad that we still have to fight for these issues -- for equal treatment for all people, for kindness and compassion,” Casey said.

Demonstrators began streaming into Washington earlier in the week.

Some wore shirts that read, “Nasty Women Unite,” a reference to the name Trump called Clinton during a presidential debate. One woman on Friday carried a sign that read, “My body is not your political playground.”

The sea of pink knit cap-wearing demonstrators included men who said they wanted to show solidarity with the women in their lives.

“It’s been a really tough two and half months — this feels like an opportunity to continue speaking up for love and equality,” said Ian Lyons, 25, a political organizer from Washington, who had worked for the campaign of Democrat Hillary Clinton.

Tyler Baranski, 27, of Washington, held a large poster of the face of young woman who could not make it to the march.

The woman had submitted her photo as part of the “Inside Out Project,” an effort to collect photos of woman throughout the country who were unable to travel for the march.

“Just to be able to hold a picture of someone who wanted to be here, but couldn’t be here, feels like I’m also representing my mother and sister, who I wish could’ve been here,” Baranski said.

“No hate, no fear, everyone is welcome here,” the marchers chanted, but the event in its planning stages wasn’t without controversy about inclusivity.

Organizers removed the anti-abortion rights feminist group New Wave Feminists of Dallas from the list of official march sponsors because they said the demonstration was pro-abortion rights. The New Wave Feminists’ founder called it ironic that the group would be excluded from an event that preached inclusivity.