Millions of people will attend memorials from sunrise to sunset across the US.

At daybreak in New York, firefighter and police pipe bands will begin marching from each of the city's five boroughs to the site of the World Trade Centre.

They will join victims' families and city leaders for a ceremony at Ground Zero where a minute of silence will be held at 8.46am to mark the moment the first plane hit the World Trade Centre.

Former mayor Rudolph Giuliani will then lead family members and a cross-section of New Yorkers, and people from around the world, in reciting the name of each victim of the twin towers attack.

Another moment of silence will be held at 10.29am, the time the second tower collapsed.

Families of the dead will then be allowed to descend by a ramp to the lowest level of the seven-storey crater where the World Trade Centre stood to leave flowers to honour their loved ones.

In Washington, victims' relatives will attend a closed service at the Pentagon, starting at 9.30am, around the time the jet ploughed into the building.

They will later be taken on a tour of the building to see a memorial set up inside the US military headquarters close to the impact point.

Thirty thousand people are expected to attend a ceremony at Shanksville, Pennsylvania, where the United flight 93, the fourth hijacked jet, crashed after passengers stormed the cockpit.

A bell will toll 44 times at the service, once for each victim.

President Bush is to visit the three attack sites during the day to pay his respects to the victims.

Elsewhere around the country, towns and communities will also mark the anniversary with special services and tributes.