Washington - Long before sunrise, with the crescent moon still high in the sky, inauguration revellers left warm homes to stand in long, cold lines and ride packed trains to the once-in-a- lifetime event unfolding Tuesday in the nation's capital.

Unprecedented numbers - the final count could reach 2 million - gathered to celebrate the presidency of Barack Obama, 47, the nation's soon-to-be first black president who many said was bringing them hope after eight gloomy years of the George W Bush presidency.

The day uncorked a level of enthusiasm for American politics and the presidency that long-time Washington residents said they had never seen.

"I'm proud of my country, and thought earlier we were drowning," said Fred Lathern, 67, a retired printer who worked for the government and was born and raised in Washington. "There's hope that Obama will pull us out."

The contrasts couldn't be greater. In 2001, Bush entered office having lost the popular vote but won a Supreme Court decision. Obama is bounding into office on a feverish upswell of expectation and a solid 53 per cent of the vote.

As much as the enthusiasm on the streets was an outpouring of support for Obama, it was also a sign people were happy to get rid of Bush, who is leaving office with the lowest job approval rating in decades.

"Goodbye Bush, Goodbye Bush," Metro riders continuously chanted at one exit station near the festivities.

Revellers travelled to Washington from all over the United States and the world to witness history in the making.

"I could have seen this on TV but I wanted to be here to see hope, change and history in the making," said Yvonne Gill, 43, a nurse from Notre Dame, Indiana.

Barriers were set up all around the downtown area to block vehicle traffic as the crowd filled bleachers along the parade route Obama will take along Pennsylvania Avenue from Capitol Hill to the White House after swearing the oath of office at 1700 GMT.

Cynthia McNeal, 50, an African American office secretary from North Carolina, said she came to honour her parents and the 1960s struggle for civil rights led by Martin Luther King Jr.

"I'm here to witness history," McNeal said.

To keep the crowds happy as they packed the 3-kilometre-long National Mall from the Lincoln Memorial to near Capitol Hill, organizers replayed the 2-hour star-studded Obama concert from Sunday afternoon.

"This is one of the most extraordinary moments in American history, where the past, present and the future come together at noon today," Congressman Jesse Jackson Junior, whose civil rights activist father ran for president in the 1980s, told Deutsche Presse-Agentur dpa.

"Today, the world will look at America differently and today Americans will look at each other differently," he said.

Obama enters office with broad support from all ethnic groups, but the moment carried particular poignance for African-Americans.

"We waited a long time to get here, but we have to be involved. It's about all of us," said Denzel Washington, the 54-year-old actor who was in the close-up viewing area.

Washington, who helped shape the image of the modern African- American on the big screen, said Obama's inauguration as the 44th US president was a tribute to the sacrifices of civil rights activists who went before him.

"There's been a lot of change to lead to this moment. Many came before him, made sacrifices for this day to happen. It's for them," he said.

High expectations for Obama to tackle the two wars and faltering economy that he is inheriting grew Tuesday along with the high spirits that pulsed through the record crowds.

Even at 7 am, groups of revellers had a hard time keeping their members together as they headed to the National Mall.

At one point, a woman looking for a group member cried out: "Jesus, where are you?"

Came the anonymous response from the crowd: "He's at the mall in a couple of hours!" (dpa)