With the world as a witness, Obama makes history
Two million people descended on the Washington Mall to witness the historic handover of power in a ceremony marked with cheers, smiles and tears.
Washington -- Barack Obama took the oath of office as the first black president in US history Tuesday, proclaiming Americans had chosen "hope over fear" and vowing to remake his nation to triumph over multiple crises at home and abroad.
In front of a jubilant two million people on Washington's National Mall, Obama, the son of a black Kenyan father and white American mother, laid his hand on the same Bible that Abraham Lincoln used at his inauguration in 1861.
"I, Barack Hussein Obama, do solemnly swear that I will execute the office of President of the United States faithfully and will to the best of my ability, preserve, protect and defend the constitution of the United States, so help me God," said Obama, provoking a huge roar from the crowd and a 21-gun salute.
Obama's inauguration, on the steps of a building erected with slave labor, broke the highest racial barrier in the United States, and may go a long way to consummating civil rights icon Martin Luther King's dream of racial unity.
"We have chosen hope over fear, unity of purpose over conflict and discord," Obama said, in a somber, sometimes poetic inaugural address shot through with optimism that the new president can lead America through its current storms.
"Starting today, we must pick ourselves up, dust ourselves off, and begin again the work of remaking America," he told a nation locked in the worst economic crisis since the 1930s Great Depression.
"Today I say to you that the challengers we face are real, they are serious and they are many," Obama said, seeking to buy himself time to haul the country out of its current woes. "They will not be met easily, or in a short span of time. But know this, America -- they will be met."
The crowd on the National Mall numbered at least two million, the Washington Post said, and many in the throng wept as the new president spoke.
Former president George W. Bush looked on as the torch of power was passed, after his turbulent eight years in the White House.
As Bush and wife Laura flew over the mall in a helicopter, many in the crowd mockingly sang "Hey Hey Hey, Goodbye."
Bush later left Andrews Air Force Base in Maryland on a jet for Texas.
In the speech, Obama also sent an immediate message to the rest of the world, and Muslim nations in particular, after America's ties with some of its top allies were tarnished during the Bush years, especially over the Iraq war.
"America is a friend of each nation and every man, woman, and child who seeks a future of peace and dignity, and that we are ready to lead once more," he said. "To the Muslim world, we seek a new way forward, based on mutual interest and mutual respect. We understand that greatness is never a given, it must be earned."
But he also warned that those who would use "terror" and slaughter innocents to threaten the United States would face an uncompromising response.
"We say to you now that our spirit is stronger and cannot be broken; you cannot outlast us, and we will defeat you."
Obama called on Americans to launch a "new era of responsibility" as the economy sinks deep into recession, brought on by massive stocks of bad mortgages and debt.
"Our nation is at war, against a far-reaching network of violence and hatred," Obama said.
"Our economy is badly weakened, a consequence of greed and irresponsibility on the part of some, but also our collective failure to mark hard choices and prepare the nation for a new age."
He also signaled a sharp shift from Bush administration anti-terror policies which critics say have compromised US ideals and the constitution.
"As for our common defense, we reject as false the choice between our safety and our ideals."
He said the United States would begin to "responsibly leave Iraq to its people and forge a hard-earned peace in Afghanistan.
The new president also said the United States would join other nations in rolling back "the specter of a warming planet."
The new president and his wife Michelle were set to leave the Capitol later Tuesday to take part in the inaugural parade, before going onto to attend a whirlwind of official balls in the evening.
Once the partying is over, Obama is expected to launch a series of policy actions this week, including an order that will set in train the closure of Bush's "war on terror" internment camp at Guantanamo Bay.
Obama's moment in history was being closely watched abroad.
British Prime Minister Gordon Brown hailed Obama's inauguration as a "new chapter in both American history and the world's history."
French President Nicolas Sarkozy said he was eager to work with Obama to "change the world" while German Chancellor Angela Merkel wished him "the best of luck."
A BBC poll of people in 17 countries found an average of two-thirds believe Obama will improve frayed relationships between the United States and the rest of the world.
But with expectations running high at home and globally, Obama's team is pleading for patience as it confronts a groaning in-tray of challenges from Gaza to Guantanamo.
Obama has vowed to hit the ground running as soon as he takes office, pushing an 825-billion-dollar stimulus package to lift the US economy and vowing to repair the tattered US image abroad. The new president has also offered talks with US foes such as Iran.