Washington - In his waning hours as a civilian Tuesday, president-elect Barack Obama sought the spiritual solace of church in a Washington thrumming with the happy cheers of human masses.

At noon (1700 GMT), Obama will become commander-in-chief of the US military as the first black US president, when he must tackle the unprecedented challenges of two wars and plummeting economy.

Following inaugural tradition, Obama, 47, and his wife Michelle, 45, dressed in a yellow sheath and matching coat, left Blair House, where White House guests stay, to attend services at nearby St John's Episcopal Church.

But however quiet it was in church, the rest of the city echoed with chants and cheers of hundreds of thousands of people who began descending on the National Mall at 4 am.

After the service, Obama, his vice-president elect Joe Biden and their spouses will be met by the special Congressional inaugural committee and be escorted across the street to the White House for a brief meeting with George and Laura Bush.

There's always plenty of speculation about what they say at that awkward moment, but little ever is leaked to the public.

Bush and Obama then will ride together to the Capitol for the swearing-in, a tradition started in 1837 and an enduring reminder that the US continues to be a country that prides itself on the peaceful transfer of power.

The formal swearing-in ceremony starts at 11:30 am (1630 GMT) on the West Front of the Capitol that overlooks the 3-kilometre-long National Mall, towards the Lincoln Memorial.

As they waited in lines that snaked around multiple city blocks for admission to roped off areas, or streamed through streets cleared of cars on their way to the open access mall, revellers showed a "spirit of congeniality," as Karen Jackson, 44, of San Francisco, noted.

Her friend had nearly fainted in the overcrowded subway train on the way downtown.

A select 240,000 people have tickets for immediate viewing of Obama's inauguration. The rest will be watching from the mall, with the help of more than a dozen jumbo TV screens.

The unprecedented crowds - more than 1 million people were expected - waited in lines that snaked around multiple city blocks for admission to roped off areas at the parade, or streamed through streets cleared of cars on their way to the open access mall.

There was a "spirit of congeniality," as Karen Jackson, 44, of San Francisco, noted.

Her friend had nearly fainted in the overcrowded subway train on the way downtown, but someone had gotten got up and gave her a seat. (dpa)