Some of the biggest names in show business got president-elect Barack Obama to dance to their tune, if only for a few minutes, two days before he will be sworn in as the 44th president of the United States.

"We Are One," a two-hour concert Sunday at the Lincoln Memorial kicked off three days of inaugural festivities, attracting hundreds of thousands of people of all ages, races and nationalities.

Washington's memorial-laden National Mall park, the site of many historical protests, was transformed into a colourful, lurching sea of cheering, singing and dancing Obama supporters. Most had waited for six to eight hours in 2-degree-Celsius weather to get a glimpse of the next president.

New Hampshire Episcopal Bishop Gene Robinson, who was named the world's first openly gay bishop in 2003, said a prayer before the concert: "Bless us with anger - at discrimination, at home and abroad, against refugees and immigrants, women, people of colour, gay, lesbian, bisexual and transgender people."

He asked for understanding "that our new president is a human being, not a messiah."

The music was punctuated by brief speeches bridging the past and future, outlining America's challenges and successes, and incorporating themes of cultural diversity, environmental protection, tolerance and hope.

"We stand on the steps of the Great Emancipator," actor Denzel Washington said at the footsteps of the monument that enshrines Abraham Lincoln, the president who freed the slaves, and the steps where Martin Luther King Jr gave his landmark "I have a dream" speech.

"On this day we're inspired by the man we have elected to be the 44th president," Washington said.

He gave way to Bruce Springsteen and a gospel choir performing The Rising, a favourite from the campaign trail that got a standing ovation from Obama and his wife, Michelle.

The star-studded lineup featured performances by Mary J Blige, James Taylor, John Bon Jovi, Sheryl Crow and John Mellencamp. But the one who seemed to rival Obama's celebrity was U2 frontman Bono, greeted with screams that echoed down the mall.

"Let freedom ring," the Irish activist-singer said. "On this spot where we're standing, 46 years ago Dr King had a dream. On Tuesday, that dream comes to pass."

U2 belted out two hits: Pride (In the Name of Love) and City of Blinding Lights, another campaign theme song.

Bono used the platform to make a political statement, calling Obama's victory: "not just an American dream but also an Irish dream, a European dream, an African dream, an Israeli dream and also a Palestinian dream."

He told Obama, who watched from the front row of a heated, glass enclosure: "What a thrill for four Irish boys from the north side of Dublin to honour you sir."

"I can't decide who to love more - Bono or Obama," said Jean Athas, 17, a student from Ohio. "Both inspire me to be a better person. I want to move the world like them. I'm here so I can tell my grandchildren that I was."

Many, like Maxine Anderson, 45, an African-American from New Orleans, Louisiana, drove 18 hours to attend the concert, fueled by a desire to witness an event she hadn't expected in her lifetime.

Andrea Ortiz, 28, eight months pregnant, joked: "I would have had a C-section to have an inauguration day baby. But I'll settle for calling him Barack."

For the teeming crowds that huddled in small circles to ward off the cold, Obama was a presence hours before he arrived - on t-shirts, buttons, caps and posters. Whenever a helicopter whirred overhead, a spontaneous cheer erupted, people thinking it was Obama's grand entrance.

One agile reveller climbed a tree on which he propped a lifesize Obama cutout. Others whiled away the time playing cards, tossing beach balls and occasionally bursting into a raucous cheer: "Obama! Obama! We're all fired up and ready to go."

The mood was convivial, celebratory and optimistic.

"I'm too happy to cry - I'll save my tears for his inauguration. Today, I'm here to dance," said Carol McClellan, 70, a grandmother of six from Indiana, who said her boisterousness was embarrassing her children.

The wait was worth it. The A-list performers sang familiar tunes that let people vociferously chime in, bobbing in their limited space.

Garth Brooks had everyone almost uncontrollable as he sang American Pie and Shout. When Usher, Shakira and Stevie Wonder took the stage to perform Higher Ground, the Obama family was clapping and dancing, too. Beyonce capped what many called a "magical" afternoon with America the Beautiful.

The actors did their bit, with Tom Hanks paying tribute to Abraham Lincoln and Marisa Tomei quoting from Ronald Reagan's inaugural address. Jamie Foxx did an excellent Obama impersonation, prompting laughter from the president-elect.

Golfing sensation Tiger Woods spoke emotionally of the military: "I am a son of a man who dedicated his life to his country, his family and the military, and I am better for it."

Actor Samuel L Jackson reminded people of the sacrifices of Rosa Parks, who in 1995 in Montgomery, Alabama, refused to give up her bus seat for a white passenger, leading to a successful, yearlong boycott by the African-American community.

Obama had the last word at the end of what he called a "celebration of American renewal."

Amid an economic crisis and wars in Afghanistan and Iraq, he refrained from sugar-coating the tasks at hand.

"In the course of our history, only a handful of generations have been asked to confront challenges as serious as the ones we face right now," Obama said.

But he insisted: "There is no obstacle that can stand in the way of millions of voices calling for change."