Washington  - One day before his inauguration as the United States' first African-American president, Barack Obama rolled up his sleeves and joined other Americans in celebrating the birthday of civil rights leader Martin Luther King Jr with acts of community service.

The outpouring of generosity comes amid final preparations in Washington for the lawmakers, dignitaries and as many as 2 million Obama supporters who were expected to flood the capital's National Mall for the swearing-in ceremony on Tuesday.

Obama hoped to turn the annual celebration of King's legacy into a "day of service" - a prominent theme during his two-year campaign for the presidency.

For African Americans, Obama's inauguration Tuesday will go a long way towards fulfilling the hopes of racial equality that King evoked in his famous "I Have A Dream" speech in 1963.

"Dr Martin Luther King's was a life lived in loving service to others," Obama said in a statement. "As we honor that legacy, it's not a day just to pause and reflect - it's a day to act."

Obama, 47, began the day visiting wounded US soldiers at Walter Reed Medical Center before touring an emergency shelter for the homeless and helping to paint one of its walls. He later planned to have a lunch with a group of community volunteers.

"Given the crisis that we are in and the hardships that so many people are going through, we cannot allow any idle hands," Obama said during his stop at the Sasha Bruce Youthwork, a shelter for teenagers. "Everybody is gonna' have to pitch in."

Obama's wife Michelle as well as vice president-elect Joe Biden and his wife Jill were out in Washington to attend other service projects. Obama said more than 5,000 such projects had been organized across the country.

In the evening, three high-profile Americans were to be honoured for their own service to the country: Colin Powell, a Republican and former US secretary of state; John McCain, Obama's Republican rival for the presidency and a Vietnam War hero; and Biden, a 36-year veteran of the US Senate.

Millions from across the country have descended on Washington to witness Obama's historic inauguration as the 44th president, filling hotel rooms as far as 400 kilometres away from the city.

The inauguration party already got underway Sunday when hundreds of thousands of people flocked to the Lincoln Memorial for a two-hour concert, the first of a series of festivities leading up to the presidential oath of office on the Capitol steps.

The star-studded lineup for the free, public show on a freezing afternoon under cloudy skies featured performances by Beyonce, Bono, Bruce Springsteen and Stevie Wonder, but the real star of the day was no singer.

Obama watched the concert with his wife Michelle and two children and received a huge ovation when he arose, waved to the crowd and strode to the podium to address the masses.

The concert was a sort of warm-up event for authorities, who are preparing for even larger crowds and even colder weather on the Mall on Tuesday. The festivities area opens for the public at 4 am Tuesday morning.

President George W Bush has no public events planned on his last day in the White House. As per tradition, Bush will accompany Obama to his swearing-in Tuesday before making a low-key departure to his Texas home. (dpa)