People's Climate March draws massive crowd to Washington, D.C. on President Trump's 100th day in office

Marchers are calling for climate action.

More than 150,000 people joined the march in Washington, according to organizers.

Organizers said the crowd size exceeded their expectations. The National Park Service issued the march a permit for 100,000 people, designating a space from 6th Street and Pennsylvania Avenue, down 3rd Street and down Jefferson Avenue to 7th Street.

By 1 p.m., the march had clearly surpassed the space by more than a dozen blocks, organizers said.

"We're blown away by the numbers," People's Climate Movement national coordinator Paul Getsos said in a statement Saturday.

"This march grew out of the relationship building among some of the country's most important progressive organizations and movements," Getsos said in a statement Saturday. "There was a simple demand -– act.

"Today's actions are not for one day or one week or one year," Getsos added.

In Washington, marchers gathered at Union Square near the Capitol at 12:30 p.m. ET before marching up Pennsylvania Avenue toward the White House. The marchers plan to then encircle the White House, calling for action.

Celebrities, including Leonardo DiCaprio, were among those marching in Washington. The actor posted a photo on Twitter after the march with a caption saying, "Honored to join Indigenous leaders and native peoples as they fight for climate justice."

ABC News' Lucien Bruggeman contributed to this report.

This is a developing story. Check back for updates.

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