US President Barack Obama, with his eyes on the exit sign in Afghanistan, took the oath of office Sunday in a small ceremony at the White House that officially begins his second term in office.

The president hopes to accelerate a process of winding down America's longest war, which began with a US invasion of Afghanistan two months after the attacks of Sept 11, 2001.

Chief Justice John Roberts administered the oath at five minutes before midday with the president using first lady Michelle Obama’s family bible. Today is the constitutionally required date for the US president to assume office. Because Jan 20 fell on a Sunday, Obama will repeat the ritual tomorrow and deliver his inaugural address at the US Capitol before a crowd of his supporters gathered on the National Mall.

Vice President Joe Biden was sworn in earlier in the day at a similar ceremony at the vice presidential residence by Supreme Court Justice Sonya Sotomayor, the first Hispanic on the court and the first to administer the oath.

Obama, 51, the nation’s first black president, has presided over an economy that is still recovering from the worst recession in a generation. While the world’s largest economy grew at a 3.1 per cent rate in the third quarter, this year will bring growth of just 2 per cent, according to the median estimate of economists.

Over the next two months his administration will engage in a fiscal debate with Republican lawmakers who hold the majority in the US House over raising the government’s $16.4 trillion borrowing limit, steps to shrink the deficit and funding federal operations.

As part of today’s ceremonies, the president and the vice president laid a wreath at the Tomb of the Unknowns at Arlington National Cemetery. Obama and his family also attended services at historic Metropolitan African Methodist Church in Washington.

Tomorrow’s public inauguration ceremony coincides with the federal holiday marking the birth of slain civil rights leader Martin Luther King. Jr Roberts will again administer the oath while using King’s traveling bible and President Abraham Lincoln’s first inaugural bible, the same one Obama used for his swearing in four years ago.

Obama kicked off four days of events tied to the inaugural by volunteering with his wife and daughters on a renovation project at a Washington elementary school. As he did four years ago, Obama called for a National Day of Service on the eve of his inauguration, saying volunteerism represents the democratic ideals upon which the country was founded.

“This is really what America’s about, this is what we celebrate,” Obama said to volunteers, after helping paint a bookshelf at the school in Northeast Washington.Today was the second time Obama has been sworn in as president by Roberts in a small White House ceremony.

Agencies add: Obama, with a slight smile, took the oath at an intimate, private ceremony in the Blue Room of the White House lasting less than a minute, raising his right arm and placing his left hand on a family Bible.

The president solemnly swore to "faithfully execute the office of President of the United States" and to "preserve, protect and defend the Constitution of the United States, so help me God."

Chief Justice Roberts, who stumbled when swearing in Obama to open his first term in 2009, read each line of the oath out loud, before the president repeated words first intoned by George Washington, 224 years ago.

After a ceremony lasting less than a minute, Obama hugged his wife, and children Malia, 14 and Sasha, 11 before quipping: "I did it" to his youngest daughter.

Obama, 51, will embark on a second term at a time of deep partisan division in Washington, and will face foreign crises testing his legacy, including Iran's nuclear program and resurgent Islamist militancy in North Africa.

Senior aide David Plouffe said the president would use his second inaugural address before an expected 500,000 plus crowd -- much smaller than in 2009 -- to stress the national truths Americans share.

"He is going to talk about how our founding principles and values can still guide us in today's modern and changing world," Plouffe said on the ABC News show "This Week."

"He is going to say that our political system does not require us to resolve all of our differences or settle all of our disputes, but it is absolutely imperative that our leaders try and seek common ground."

Obama's second inauguration, which comes courtesy of an election win over Republican Mitt Romney in November, lacks the historical resonance of January 20, 2009, when he was sworn in as the first black American president.

Since then, a graying Obama has struggled to accelerate a weak economic recovery, failed to meet hugely elevated expectations for his presidency and waged a political war of attrition with Republicans.

He begins anew with several fierce budget battles looming in Congress, and his "Yes We Can" rhetoric soured by sarcasm over the blocking tactics of Republicans in the partisan brouhaha paralyzing government in Washington.

Abroad, the US confrontation with Iran is fast-headed to a critical point with the specter of military action becoming ever more real the longer diplomacy over Tehran's nuclear program remains stuck in neutral.

And terror strikes that killed Americans in Benghazi and Algeria call into question Obama's election year sound bite that "Al-Qaeda is on the run," despite the killing of Osama bin Laden in Pakistan in 2011.

Muscle-flexing by China and rising tensions in contested waters with its neighbors, as well as North Korea's nuclear belligerence, will meanwhile test the president's signature pivot of US diplomacy to Asia.