WASHINGTON — Saying that "We are transferring power from Washington, D.C., and giving it back to you, the people," New York real estate mogul Donald Trump was sworn in as the nation's 45th president Friday.

Demonstrators protesting Trump's election later clashed with Washington, D.C., police, leading to scores of arrests.

Ten weeks after winning the presidency in an historic upset, Trump was inaugurated on the steps of the U.S. Capitol Building in front of hundreds of thousands on the National Mall as the clock struck noon.

In his 18-minute inaugural address, the former reality TV star promised to deliver on the populist themes of his presidential campaign.

"For too long, a small group in Washington has reaped the rewards of government while the people have borne the cost," Trump told the crowd. "That all changes starting right here and right now. January 20 will be remembered as they day the people become the rulers of this nation again."

"The forgotten men and women of this country will be forgotten no longer," he said. "From this day forward, a new vision will govern our land: America First. Every decision will be made to protect American citizens and American workers."

"When you open your heart to patriotism, there is no room for prejudice," Trump added. "Whether we are black or brown or white, we all bleed the red blood of patriots."

"And yes, together we will make America great again."

Around two hours later, District of Columbia police used tear gas in an effort to disperse more than 1,000 protesters who had gathered downtown. Protesters threw bricks, and a fire was set at one point. The Associated Press also reported that several motorists were caught in the clash.

In another demonstration prior to the ceremony, protesters denouncing Trump clashed with police as authorities cordoned off about 100 demonstrators. Police used what appeared to be pepper spray as protesters chanted, "Hands up, don't shoot" while a helicopter hovered overhead.

Posts on social media showed some demonstrators forming human chains and chanting phrases like "Not my president."

In all, reports say at least 217 protesters were arrested, and six officers suffered minor injuries.

In New York, demonstrators marched peacefully from Foley Square to the Trump Building Friday evening.

Additional protest events were scheduled to take place in New York and Washington on Saturday.

Following the inauguration, a luncheon was held for the new president and vice president. 

It took place at Statuary Hall, where he applauded many of his cabinet appointees.

Trump also called for unity between Democrats and Republicans following a contentious election last year. 

"We're all dealing together. We all want the same thing. We're all good people. And whether you're a Republican or Democrat, it doesn't make any difference. We're going to get along," Trump said.

After being sworn in, Trump, his wife, and his son Barron rode the presidential limo in the inaugural parade along Pennsylvania Avenue.

The new president and his family got out of the limo at two points along the parade to wave to the crowds.

The parade featured more than 8,000 participants, including marching bands and veterans' groups.

Some anti-Trump protesters were also on hand on the sidewalks as the First Couple walked the parade route.

Trump capped his day by attending three inaugural balls in Washington.

Revelers began gathering early Friday morning to stake out a spot on the National Mall in order to watch the festivities. Before the ceremony, cheers went up from many in attendance when images appeared on viewing screens of Sen. Bernie Sanders and outgoing First Lady Michelle Obama.

Outgoing President Barack Obama departed the capital by helicopter following the ceremony at 12:45 p.m. EST.

Speaking at Joint Base Andrews, he reflected on his time in office.

"This is not a period," he said. "This is a comma in the continuing story of building America."

He and his family are slated to leave for California for vacation before they return to Washington D.C. as private citizens. 

Trump and his wife Melania began the day attending mass with Vice President-elect Mike Pence and their families at St. John's Church.

Trump then traveled to the White House, where he was greeted by the Obamas.