It may be -6C, but not even the decidedly chilly Washington weather could stop crowds of people forming this morning in anticipation of Barack Obama's inauguration.

As early as 4am - some eight hours before the swearing in of the new president - people were lining up at the city's underground stations, waiting for trains to take them closer to the action.

Estimates of the total crowd expected range from 1 million upwards, with the attendance likely to top the previous record for an inauguration.

In a first for a swearing in ceremony, the entire National Mall - the park leading up to the Lincoln Memorial - has been opened to the public.

And from the early hours, the park begin to fill with expectant Obama supporters.

The sheer number of people have put pressure on the city's infrastructure.

Out-of-towners and Washington residents alike overwhelmed the transport and filled city streets. Tens of thousands of people turning Washington's orderly grid of streets into a festive party scene throughout the morning.

Obama activist Akin Salawu, 34, of Brooklyn, New York, was one of the early arrivals.

The community organiser and web producer said: "This is the culmination of two years of work.

"We got on board when Obama was the little engine who could. He's like a child you've held onto. Now he's going out into the world."

Streets around the Capitol building quickly filled in the early hours, with security checkpoints inundated with people.

Warming tents and other facilities on the Mall were late opening because of traffic problems, while crowds delayed staffers from reaching them.

Meanwhile, ticket holders approaching the inaugural site on Capitol Hill were themselves delayed by security checks.

Connie Grant, of Birmingham, Alabama, said she got up at 3.30am after coming to Washington with a group.

Three hours later she was still waiting for police to clear the way into the Mall.

Despite the delays, people queuing up to attend remained good natured.

Ms Grant said: "I sacrificed and came here. To me, this is very historic. I just wanted to be here."

Christian Alderson, of Berryville, Virginia, said he was in Memphis, Tennessee when Martin Luther King Jr. was assassinated.

The 73-year-old said: "That day was sorrowful. This is a dream come true for me."

Police in the city have projected inaugural crowds between one million and two million.

The previous record for an inauguration was for Lyndon B Johnson in 1965. Around 1.2 million people turned up to see Johnson sworn in as president.